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TMS Aurelius
Documentation
July 2017
Copyright (c) 2017 by tmssoftware.com bvba
E-mail: [email protected]
http://www.tmssoftware.com
TMS Aurelius Documentation
Table of Contents
Chapter I Introduction
Chapter II Getting Started
Chapter III Database Connectivity
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Chapter IV Mapping
(c) 2016 TMS Software
47
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TMS Aurelius Documentation
Chapter V Multi-Model Design
Chapter VI Manipulating Objects
(c) 2016 TMS Software
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TMS Aurelius Documentation
Chapter VII Queries 128
(c) 2016 TMS Software III
TMS Aurelius Documentation
Chapter VIII Data Binding - TAureliusDataset 164
(c) 2016 TMS Software IV
TMS Aurelius Documentation
Chapter IX Distributed Applications
Chapter X Events
186
196
Chapter XI Advanced Topics 206
(c) 2016 TMS Software V
Chapter
Introduction
I
TMS Aurelius Documentation
1 Introduction
TMS Aurelius is an Object-Relational Mapping (ORM) framework. Its purpose is to be the definitive ORM framewok for the Delphi environment, with full support for data manipulation, complex and advanced queries, inheritance, polymorphism, among others. This manual covers all topics needed for you to know about Aurelius and start using it.
TMS Aurelius product page: http://www.tmssoftware.com/site/aurelius.asp
TMS Software site: http://www.tmssoftware.com
Manual Topics
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Introduction
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Components and Databases Homologation
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Database Manager - Creating the Schema
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(c) 2016 TMS Software 2
TMS Aurelius Documentation
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Data Binding - TAureliusDataset
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JSON - JavaScript Object Notation
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(c) 2016 TMS Software 3
TMS Aurelius Documentation
1.1
Benefits
Aurelius brings all benefits an application can obtain from using an ORM framework. Main ones are:
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Productivity: Avoid complex SQL statements that can only be verified at runtime. Code directly with objects.
Instead of this code:
Query1.Sql.Text := 'SELECT I.ID AS INVOICE_ID, I.INVOICE_TYPE,
I.INVOICENO, I.ISSUE_DATE, I.PRINT_DATE, ' +
'C.ID AS CUSTOMER_ID, C.CUSTOMER_NAME, C.SEX, C.BIRTHDAY, N.ID
AS COUNTRY_ID, N.COUNTRY_NAME' +
'FROM INVOICE AS I INNER JOIN CUSTOMER AS C ON (C.ID =
I.CUSTOMER_ID) ' +
'LEFT JOIN COUNTRY AS N ON (N.ID = C.COUNTRY_ID)' +
'WHERE I.ID = :INVOICE_ID;'
Query1.ParamByName( 'INVOICE_ID' ).AsInteger := 1 ;
Query1.Open;
ShowMessage(Format( 'Invoice No: %d, Customer: %s, Country: %s' ,
[Query1.FieldByName( 'INVOICE_ID' ).AsInteger,
Query1.FieldByName( 'CUSTOMER_NAME' ).AsString,
Query1.FieldByName( 'COUNTRY_NAME' ).AsString]));
Write this code:
Invoice := Manager1.Find<TInvoice>( 1 );
ShowMessage(Format( 'Invoice No: %d, Customer: %s, Country: %s' ,
[Invoice.InvoiceNo, Invoice.Customer.Name,
Invoice.Customer.Country.Name]));
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Maintainability: Clearer business logic by dealing with objects, hiding all the database-access layer.
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Portability: Easily change the underlying database - all your business code stays the same since they are just pure objects.
1.2
Features
Here is a list of main features of TMS Aurelius framework:
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Several
supported (MS SQL Server, Firebird, MySQL)
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Several
supported (dbExpress, AnyDac,
SQLDirect, UniDac, ADO)
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Multi-platform solution - Win32, Win64, Mac OS X, VCL, FireMonkey
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loading of entity objects in an object-oriented way
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Queries - Powerful query API using criteria expressions, projections, grouping,
conditions and even logical operators in a LINQ-like approach
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Inheritance mapping and polymorphism - map a full class hierarchy into the
database
(c) 2016 TMS Software 4
TMS Aurelius Documentation
·
Visual data binding with data-aware controls using full-featured
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Cross-database development - use a single Delphi code to target multiple databases in a transparent way
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Choose from classes-to-database approach (
creating the database structure
from classes) or database-to-classes approach (creating classes source code from database, using TMS Data Modeler)
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Mapping directly in classes using custom attributes
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Lifetime management of objects using object manager
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Cached and
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Automatic
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Lazy loading for associations and
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Allows logging of SQL commands
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Allows
mapping enumerated types to database values
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Open architecture - easy extendable to use different component sets or database servers
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Available for Delphi 2010 and up.
1.3
What's New
Version 3.9 (Jul-2017)
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New: TCriteria.Refreshing method
. Using Refreshing method when creating
an Aurelius query will force entities returned by the query to be refreshed even if they are already cached in Object Manager.
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. In addition to unique indexes, you can now specify
non-unique index (for optimization purposes) with this attribute and Aurelius will create it automatically upon database schema update.
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New: TAureliusDataset.SyncSubprops property
of associated fields. When an entity field (e.g., "Customer") of the
TAureliusDataset component is modified, all the subproperty fields (e.g.,
"Customer.Name", "Customer.Birthday") will be automatically updated with new values if this property is set to True.
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New: TAureliusDataset.SubpropsDepth property
of subproperty fields. When loading field definitions for TAureliusDataset at design-time, or when opening the TAureliusDataset without persistent fields, one TField for each property in object will be created. By increasing
SubpropsDepth to 1 or more, TAureliusDataset will also automatically include subproperty fields for each property in each association, up to the level indicated by SubpropsDepth.
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New: TAureliusDataset.DefaultsFromObject property
values with object state. When inserting a new record in TAureliusDataset, all fields come with null values by default. By setting this property to True, default (initial) value of the fields will come from the property values of the underlying object.
(c) 2016 TMS Software 5
TMS Aurelius Documentation
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New: TObjectManager.FindCached and IsCached methods
methods allow checking if an object of specified class and id is present in the object manager cache, without hitting the database to load the object.
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New: TAureliusDataset popup menu option at design-time for quick
reloading field definitions. At design-time, if you right-click
TAureliusDataset component, a new menu "Reload from <class>" appear for quickly reloading the field definitions for a previously loaded class.
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Improved: Faster lazy-loading of proxied associations in some situations.
When the association has a JoinColumn attribute with a explicity param value for ReferencedColumnName, the manager was always hitting the database to load associated proxy. Now if the referenced column is an id column, the manager will first check if associated object is already in cache.
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Improved: TAureliusDataset doesn't automatically call Flush anymore on
Insert and Delete operations, when Manager property is set. Only Save and
Remove methods are called, respectively. This fixes performance and unexpected behaviors in some scenarios, but might break existing code. It's a breaking change.
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Improved: When targeting DB2 databases, TDatabaseManager now retrieves schema of database objects and updates/creates them accordingly.
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Improved: Updating ElevateDB database schema
(TDatabaseManager.UpdateDatabase) is significantly faster now.
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Fixed: Calling TAureliusDataset.Delete was raising an exception in some specific situations.
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Fixed: Argument out of range on specific Merge operations. This error was happening when merging an object A with a proxied list of B objects. If the B objects happen to have a reference back to A, then another instance of A would be loaded, the proxied list would be loaded, and such list would override the list of original object A being merged, causing this error.
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Fixed: Firedac + Oracle on Delphi Tokyo was causing "Data Too Large" error on fixed-sized parameters.
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Fixed: Calling TAureliusDataset.RecordCount on a closed dataset was raising an Access Violation.
version 3.8 (May-2017)
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Fixed: Using AureliusDataset, during an insert, if a Post operation failed, an
Access Violation would be raised if user cancels insertion of record.
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Fixed: Access Violation when loading a lazy blob in the handler of OnDeleted event
version 3.7 (Mar-2017)
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New: Linux platform support together with Rad Studio 10.2 Tokyo support
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Fixed: Memory leaks in mobile platforms
(c) 2016 TMS Software 6
TMS Aurelius Documentation
·
Fixed: Error when loading entities with inheritance where a lazy blob field is declared in an inherited class.
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Fixed: TGlobalConfigs.GetInstance.SimuleStatements not working
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Fixed: Better transactions handling on UIB (Universal Interbase) driver
version 3.6 (Feb-2017)
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New: Manager events
,
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Improved: Not equal (<>) operator support in Linq queries
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Fixed: Firebird schema update was trying to generate sequences even though they already existed in database (regression)
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Fixed: Error inserting records in SQL Server when table name ends with
"Values"
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Fixed: JSON Deserializer failed when deserializing nullable enumerated values
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Fixed: DB2 dialect was not supporting schemas (regression)
version 3.5 (Jan-2017)
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New:
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New: MSSQL dialect
UseBoolean property allows using BIT data type for
boolean fields in SQL Server
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Improved: Column names can now be mapped using double quotes
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Improved: Demos rewritten to better show use more recent Aurelius features
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Improved: Better error handling when SQLite DLL is not available
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Fixed: Error with field names containing spaces.
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Fixed: Wrong behavior and cast errors in TAureliusDataset when moving dbgrid field columns linked to the dataset
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Fixed: Cast error in Aurelius Dataset when setting a nullable enumerated field to null
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Fixed: Aurelius Dataset Locate method accepts variant array as search value even when locating for a single field
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Fixed: IBExpress adapter not working if using the overloaded Create constructor that receives a TComponent parameter
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Fixed: Memory leaks on nextgen (mobile) platforms when using FireDac
(version 3.4.1)
version 3.4 (Sep-2016)
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New:
Linq query syntax improved with support for relational operators:
Linq['Name'] = 'Mia'. All query examples in this documentation updated to newer syntax.
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New: Arithmetic projections
Subtract , Multiply and Divide , also
supporting operators: Linq['Total'] + Linq['Additional']
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New:
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New: Linq "type-helper" version all existing functions, like
(Linq['Name'].Upper = 'MIA') and (Linq['CreatedAt'].Year = 2015)
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New: Cross-database
Concat function: Linq.Concat(Linq['FirstName'],
Linq['LastName'])
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New: Linq functions
projections: Linq['Name'].StartsWith(Linq['OtherField'])
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New: TDatabaseManager.IgnoreConstraintName property for better control of
database schema update and validation
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Fixed: ZeosLib depending on unnecessary units
version 3.3 (Aug-2016)
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New:
method can now receive an entity as parameter
allowing flushing a single entity.
(c) 2016 TMS Software 7
TMS Aurelius Documentation
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New: Support for
ZeosLib database-access components
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New:
TCascadeType.Flush cascade type allows control of how associated
objects will be flushed when flushing a single entity
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Improved: When retrieving Int64 values from database, it now tries to handle the value even when the underlying db access component provides the value as float
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Fixed: TAureliusDataset.RecNo returning wrong value when in insert mode
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Fixed: When using bidirectional associations, in some rare situations the many-to-one side of association was being cleared
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Fixed: TAureliusDataset displaying wrong records when using Filter in a detail dataset (DatasetField pointing to another dataset)
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version 3.2 (Jul-2016)
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New:
TCriteria.Clone method allows cloning an existing Aurelius criteria
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New:
TAureliusDataset.IncludeUnmappedObjects
list fields even if they are not mapped in class
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New:
event that is fired for every SQL
statement executed in database
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Improved: Mapping table and field names with spaces is now allowed, without needing to quote the names in quotes in mapping
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Improved:
updated with links for new videos and articles
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Fixed:
: Merging transient objects with proxy collections
was ignoring the collection content.
TObjectManager.MergeListLegacyBehavior
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Fixed:
: Updating/Merging objects with proxied associations
that were not modified was not clearing the value
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Fixed: "Duplicate Field Name" error in Aurelius Dataset when loaded object had properties that have been redeclared from an ancestor class
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Fixed: Inheritance using discriminator failed in some situations with SQLite due to int32/int64 type mismatch
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Fixed: DB Connection Wizard failed when using AnyDac connection
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Fixed: TProjections.Count failed for counting GUID fields
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Fixed: TDateTime field values losing time part when using dbGO and ODBC driver
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version 3.1 (May-2016)
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New: Delphi 10.1 Berlin support
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New: Explorer.ObjectFactory and Manager.ObjectFactory properties allows defing a custom
object factory for creating entity classes.
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Fixed: Database update using table schema now working with PostgreSQL and MS SQL Server
version 3.0 (Feb-2016)
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New:
Design-time wizard "New TMS Aurelius Connection" makes it very
straightforward to create Aurelius
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New:
method
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Improved:
now sets generator to
type TGuid
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Improved:
has a new overload that accepts TGuid value for id
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Improved: Saving an object with user-assigned id was calling SQL to retrieve
ID without need
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Improved: TDatabaseManager can receive a TArray<TMappingExplorer>, allowing to create the database structure for all of them at once
(c) 2016 TMS Software 8
TMS Aurelius Documentation
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Fixed: Merging an object with a lazy-loaded list wouldn't delete removed items on Flush if the object being merged was not loaded from
TObjectManager
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Fixed: After Mapping Explorer raised an error about wrong mapping when retrieving columns for a class, it could later not raise that error anymore
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Fixed: Wrong error message (AV) when opening a cursor and SQL dialect is not registered
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Fixed: Sporadic AV when destroying TAureliusDataset without closing it
version 2.9 (Oct-2015)
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New: Optimistic
versioned concurrency control of entities using
attribute
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New:
TObjectManager.UseTransactions
property allows control whether
manager uses transactions to perform internal operations. This is a
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Improved: More detailed error message when loading a proxy fails due to duplicated records
version 2.8.1 (Sep-2015)
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New: Delphi 10 Seattle support
version 2.8 (Aug-2015)
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New: Cross-database, high-level projection functions in Aurelius
Date/time functions added:
,
. String functions added:
,
.
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New: Additional TLinq conditions for string comparison:
.
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New:
OnInserted event parameters now include Master that hold the parent
instance in case of unidirectional items being inserted
version 2.7.1 (May-2015)
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Fixed: AV when using Update event listener for objects in manager without previous state (using Update method)
version 2.7 (Apr-2015)
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New:
allows subscribing listeners to respond to several events
(e.g, when an entity is inserted, updated, etc.)
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Improved: When deserializing objects from JSON, properties unknown to the entity will now be ignored, instead of raising an error.
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Improved: Music Library demo includes an audit log viewer that illustrates usage of the events system.
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Fixed: FireDAC driver not compiling on XE8
version 2.6.3 (Apr-2015)
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New: Delphi XE8 support
version 2.6.2 (Mar-2015)
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Improved: TBlob handling of data (especially using AsBytes property) improved for better performance
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Improved: TBlob.Data property removed. Breaking change
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Fixed: Flush not updating properties modified if lazy proxy/blob is loaded after properties were modified
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Fixed: Setting a lazy TBlob content that was not yet loaded didn't change blob content
(c) 2016 TMS Software 9
TMS Aurelius Documentation
·
Fixed: TAureliusDataset now retrieves correct value for RecordCount when dataset is filtered
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Fixed: Rare Access Violation when reloading associated object lists that exist in object manager
version 2.6.1 (Feb-2015)
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Improved:
TAureliusDataset design-time dialog
now makes it much easier to find a class by providing a search box
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Improved: TAureliusDataset makes it easy to reload fields from classes at design-time by remembering the last class used to load fields
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Fixed: TObjectManager.Merge was not updating collections when none of parent object properties was changed
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Fixed: AV when loading a proxy value after an object refresh
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Fixed: Error when inserting records with identity Id on tables with INSERT triggers in MS SQL Server
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Fixed: Access Violation when destroying entity objects before destroying a
TAureliusDataset component
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Fixed: Rare error when inserting records in MS SQL Server, using SQL-Direct and native SQL Server client
version 2.6 (Dec-2014)
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New:
method allows removing an object instance from
the manager without destroying it.
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New:
TFetchMode option in CreateAlias allows per-query setting for eager-
loading associations to improve performance
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New: TAureliusDataset.Current now returns an object
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New:
TAureliusDataset.ParentManager
allows fine-grained control over the
manager used in detail datasets
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New:
provides an easier, alternative way to
TCriteria.AddOrder to specify criteria order
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Improved: Automatic destruction of
when using SetSourceCriteria or SetSourceCursor
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Improved: Removed an extra final SQL being executed in paged queries using
TAureliusDataset
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Fixed: Design-time error using TAureliusDataset when recompiling packages with entities.
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Fixed: TAureliusDataset.BookmarkValid was wrongly returning true after the bookmarked record was deleted.
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Fixed: Blobs and associations being loaded in lazy mode were causing objects to be updated on flush
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Fixed: Json serialization using SuperObject was providing wrong boolean value
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Fixed: Saving child objects using unidirectional ManyValuedAssociation when parent has composite key
version 2.5 (Oct-2014)
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New:
Multi-model design architecture allows different mapping models in a
single application with a few lines of code, just by using attributes
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New:
SmartGuid generator allows using identifiers with sequential GUID for
better database performance
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New:
OrderBy attribute allows defining a default order for
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New:
Model attribute to specify the model where the class belongs to.
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New:
RegisterEntity procedure helps registering a mapped class avoiding
linker optimization to remove it from application
(c) 2016 TMS Software 10
TMS Aurelius Documentation
·
New:
property
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Improved: More detailed manager error messages when trying to save objects that are already persistent
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Fixed: Identity conflict when using MS SQL Server with multiple simultaneous sessions inserting in the same table
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Fixed: Trailing semi-comma from some PostgreSQL commands were causing errors when using FireDac with automatic record count
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Fixed: wrong data for fields OldValue property when dataset is empty
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Fixed: Incompatibility between TAureliusDataset and FastReport design-time editor
version 2.4.1 (Sep-2014)
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New: Delphi XE7 support
version 2.4 (Jul-2014)
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New: TObjectManager.Refresh method allows
database
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New:
ForeignKey attribute to define the name of foreign keys in the database
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New:
allow automatic deletion/removal of
child entities on Flush if they are removed from a parent collection
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New:
TCustomJsonDeserializer.Entities
property allows retrieving the list of
objects created by the JSON deserializer
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New: TDriverConnectionAdapter<T>.Connection property allows
referencing the original database component used for the connection
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New:
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New: TFirebirdSQLGenerator.WideStringCharSet property allows defining specific column character set for WideString properties in Firebird
·
Improved:
now can receive objects with no id. This will automatically create a copy of the object and save it. This is a
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Improved: Better performance and memory consumption using unidirectional datasets to fetch data with some specific component adapters
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Fixed: Error when updating objects with composite id in SQLite and one of id values is null
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Fixed: Error when serializing a newly created entity (not loaded with manager) with a TBlob property that has not been initialized
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Fixed: ElevateDB driver compile error when using latest ElevateDB versions
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Fixed: Error when deserializing empty dynamic array properties
version 2.3.1 (Apr-2014)
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New: Delphi XE6 Support
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Improved: MappedClasses.RegisterClass now checks if the class being registered is a valid entity ([Entity] attribute present)
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Improved: CascadeTypeAllButRemove constant makes easier to define association cascade with all options except TCascadeType.Remove
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Fixed: Using [Automapping] attribute with classes that inherit from nonentity classes was causing "Id attribute not found" error.
·
Fixed: Wrong TAureliusDataset behavior with db visual controls that rely on
CompareBookmarks method.
version 2.3 (Feb-2014)
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New: Support for Android platform
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New: Support for
components
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New: Overloaded constructor for
allows easier memory management when using data modules
(c) 2016 TMS Software 11
TMS Aurelius Documentation
·
Improved: Property TIBObjectsConnectionAdapter.Transaction allows you to change the default transaction in an IBObjects connection adapter
·
Fixed: TAureliusDataset.Current method was returning an invalid value when it was in insert state.
·
Fixed: "Duplicates not allowed" when retrieving objects in a inheritance tree where different descendant classes had associations with same name
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Fixed: TAureliusDataset missing the current record position in some situations
·
Fixed: Memory leak when trying to save unmapped objects.
version 2.2 (Oct-2013)
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New: Increased querying capabilities with new TExpression/TLinq methods that allow
comparing a projection to any other projection
(in addition to comparing to values only)
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New: Support for Rad Studio XE5
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New:
Connection driver for XData RemoteDB
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New: TCriteria.AutoDestroy property allows
keeping TCriteria in memory after
objects are retrieved
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Changed: Packages structure. See
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Fixed: Error when deserializing a Json array representing an existing object list, when class member was a proxy
·
Fixed: Exception not being raised when calling
TClassHierarchyExplorer.GetAllSubClasses
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Fixed: Wrong default values when inserting a record in XE4 with
TAureliusDataset
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Fixed: IBObjects driver now correctly performing statements using IB_Session object specified in the TIBODatabase
version 2.1 (May-2013)
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New: Full iOS support, including native access to SQLite database
·
New: Support for Rad Studio XE4
·
Fixed: Not possible to create unique keys referencing columns declared using
ForeignJoinColumn attributes
·
Fixed: Merge cascades not being applied correctly
·
Fixed: Access violation when loading package multiple times in
TAureliusDataset design-time editor
·
Fixed: Wrong example in documentation about lazy-loading associations in distributed applications (proxy loader)
·
Fixed: Schema validation example code in manual
·
Fixed: Error using transactions with IBExpress, IBObjects and
DirectOracleAccess components
·
Changed: Live bindings disabled by default
version 2.0 (Apr-2013)
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New:
Update Database Schema feature (TDatabaseManager.UpdateDatabase
method)
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New:
Database Schema validation feature
(TDatabaseManager.ValidateDatabase method)
·
New:
analysis when updating/validating/creating
(TDatabaseManager properties: Actions, Warnings Errors)
·
New:
property allows defining different class
entities for different setups (and thus databases/connections)
·
New:
TDatabaseManager.SQLExecutionEnabled property
allows generating scripts to update/create/drop database schema without effectively execute statements
(c) 2016 TMS Software 12
TMS Aurelius Documentation
·
New: TSQLiteNativeConnectionAdapter.
DisableForeignKeys methods allow control when foreign keys are enforced in
SQLite connections
·
Improved:
TGlobalConfig.AutoSearchMappedClasses
·
Fixed: Conversion error in TAureliusDataset entity fields when using live bindings
version 1.9 (Feb-2013)
·
New: Support for
Unified Interbase (UIB) components
·
Improved: Statements to generate MS SQL Server database structure now explicitly declare NULL constraint when creating fields
·
Improved: Auto mapping now automatically includes TColumnProp.NoUpdate
in ID column properties
·
Improved: Retrieving objects (Find) with null id in database now raises an exception instead of just returning a nil instance
·
Fixed: Error when flushing objects with many-valued-association declared before id fields and which foreign key field had same name as id field
·
Fixed: Cascade not being applied when flushing objects with single-valued associations pointing to unmanaged (transient) instances
·
Fixed: Exception when setting TAureliusDataset.Filtered := true when dataset is active
·
Fixed: Specific conversion issue when retrieving TGuid value from
UNIQUEIDENTIFIER fields, using SQL-Direct with server type set to stSQLServer
·
Fixed: Error when deserializing Nullable<double> types using JSON deserializer
·
Fixed: Uses clause in Direct Oracle Access driver included a wrong unit name
version 1.8 (Jan-2013)
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New: Support for
Direct Oracle Access components
·
Improved: Updated source code to work correctly When recompiling with
Assertions off
·
Fixed: Error using TAureliusDataset.Locate with nullable string fields when there were null fields in dataset
·
Fixed: Rare memory leak when using some specific compiler settings
(Optimizations=On)
·
Fixed: Memory leak in "Getting Started" demo
version 1.7 (Dec-2012)
·
New: Full
JSON support makes it easy to build distributed applications
·
New:
as string now possible in TAureliusDataset by using field name sufix ".EnumName"
·
Improved:
·
Improved:
.AutoMappingDefaultCascade now split in two different properties for Association and ManyValuedAssociation (breaking change)
·
Fixed: TGuid properties and fields were causing occasional errors in Flush method calls
version 1.6 (Sep-2012)
·
New: Delphi XE3 support
·
New: Support for
·
New:
TCriteria.RemovingDuplicatedEntities
allows removing duplicated objects from result list
(c) 2016 TMS Software 13
TMS Aurelius Documentation
·
New: Properties Count and PropNames in
TCriteriaResult object provides
additional info about retrieved projections
·
Improved: Better support for other date types (string and julian) in SQLite database
·
Improved: Possibility to use descendants of TList<T>/TObjectList<T> for many-valued associations
·
Improved: Non-generic
class type as parameter
·
Fixed: Memory leak when creating a default TMappingExplorer
·
Fixed: Error when saving collection items belonging to a joined-tables class hierarchy
·
Fixed: Cascade removal was not removing lazy-loaded associations if the associations were not loaded
version 1.5 (Jun-2012)
·
New:
Guid , Uuid38 , Uuid36 and Uuid32
identifier generators allow client-side automatic generation of GUID and/or string identifiers
·
New:
syntax to a query, increasing flexibility in query construction
·
New: Support for properties/fields of type TGuid, which are now mapped to database Guid/Uniqueidentifier fields (if supported by database) or database string fields
·
New: Support for
version 1.4 (May-2012)
·
New:
allows mapping to database columns at runtime
·
Improved: TCriteriaResult object can retrieved
projected values by projection alias
·
Improved: TCriteriaResult objects
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Improved: Better validation of MappedBy parameter in ManyValuedAssociation attribute
·
Improved: TAureliusDataset.Post method now saves object if it's not persisted, even in edit mode
·
Fixed: Issue with association as part of composite id when multiple associations are used in cascaded objects
·
Fixed: Manual Quick Start example updated with correct code
·
Fixed: Automapping was not correctly defining table name in some situations with inherited classes
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version 1.3 (Mar-2012)
·
New:
using TAureliusDataset.SetSourceCriteria
allows fetching TDataset records on demand without keeping an open database connection
·
New:
on TAureliusDataset, by using
SetSourceCursor method
·
New:
Support for ElevateDB database server
·
New:
now supported by using new TCriteria methods
Skip and Take
·
New: TCriteria.Open method allows returning a
cursor for fetching objects on demand
·
New:
TBlob .LoadFromStream and SaveToStream methods for improved blob
manipulation
·
New: "Not" operator supported in TLinq expressions and "Not_" method in
TExpression
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TMS Aurelius Documentation
1.4
·
New:
TAureliusDataset.InternalList property allows access to the internal
object list
·
Improved: TObjectManager.Find<T> method introduced as an alias for
CreateCriteria<T> method for
·
Improved: TCriteria.
UniqueResult now returns nil if no objects are returned
·
Improved: TCriteria.UniqueResult returns the unique object even if the object is returned in more than one row (duplicated rows of same object)
·
Improved:
NexusDB through UniDac components now supported
version 1.2 (Mar-2012)
·
New: Fully documented
TAureliusDataset component for visual binding
objects to data-aware controls.
·
New: Support for
·
Improved: Better error handling with more detailed and typed exceptions being raised at key points, especially value conversion routines
·
Improved: IBObjects adapter now can adapt any TIB_Connection component, not only TIBODatabase ones
·
Improved: Better exception messages for convert error when load entity property values from database
·
Fixed: issue with SQL statement when using more than 26 eager-loading associations
·
Fixed: Issue when selecting objects with non-required associations and required sub-associations
·
Fixed: Issue with lazy-loaded proxies using non-id columns as foreign keys
·
Fixed: adding Automapping attribute was not requiring Entity attribute to be declared
·
Fixed: Automapping in a subclass in a single-table hierarchy caused issues when creating database schema
·
Fixed: Memory leak in MusicLibrary demo
version 1.1 (Feb-2012)
·
New: TObjectDataset preview (for registered users only)
·
New: Support for IBObjects components
·
Improved: MusicLibrary demo refactored to use best-designed controllers
·
Improved: Access Violation replaced by descriptive error message when SQL dialect was not found for connection
·
Fixed: Registered version installer sometimes not correctly detecting XE/XE2 installation
·
Fixed: Memory leak is some specific situations with automapped associations
·
Fixed: Default value of OwnsObjects property in TObjectManager changed from false to true (as stated by documentation)
·
Fixed: Memory leak in MusicLibrary demo
·
Fixed: Component adapter was ignoring explicitly specified SQL dialect
·
Fixed: Issue with automapping self-referenced associations
version 1.0 (Jan-2012)
·
First public release
Copyright Notice
TMS Aurelius framework trial version is free for use in non-commercial applications, that is any software that is not being sold in one or another way or that does not generate income in any way by the use of the application.
(c) 2016 TMS Software 15
TMS Aurelius Documentation
1.5
For use in commercial applications, you must purchase a single license, a small team license or a site license. A site license allows an unlimited number of developers within the company holding the license to use the components for commercial application development and to obtain free updates for a full version cycle and priority email support. A single developer license allows ONE developer within a company to use the components for commercial application development, to obtain free updates and priority email support. A small team license allows TWO developers within a company to use the components for commercial application development, to obtain free updates and priority email support. Single developer and small team licenses are NOT transferable to another developer within the company or to a developer from another company. All licenses allow royalty free use of the components when used in binary compiled applications.
The component cannot be distributed in any other way except through TMS
Software web site. Any other way of distribution must have written authorization of the author.
Online registration for TMS Aurelius is available at http:// www.tmssoftware.com. Source code & license is sent immediately upon receipt of check or registration by email.
TMS Aurelius is Copyright © 2012 TMS Software. ALL RIGHTS RESERVED.
No part of this help may be reproduced, stored in any retrieval system, copied or modified, transmitted in any form or by any means electronic or mechanical, including photocopying and recording for purposes others than the purchaser's personal use.
Getting Support
General notes
Before contacting support:
- Make sure to read this whole manual and any readme.txt or install.txt files in component distributions, if available.
- Search TMS support forum and TMS newsgroups to see if you question hasn't been already answer.
- Make sure you have the latest version of the component(s).
When contacting support:
- Specify with which component is causing the problem.
- Specify which Delphi or C++Builder version you're using and preferably also on which OS.
- For registered users, use the special priority support email address
(mentioned in registration email) & provide your registration email & code. This will guarantee the fastest route to a solution.
- Send email from an email account that
1) allows to receive replies sent from our server
2) allows to receive ZIP file attachments
3) has a properly specified & working reply address
Getting support
(c) 2016 TMS Software 16
TMS Aurelius Documentation
1.6
For general information: [email protected]
Fax: +32-56-359696
For all questions, comments, problems and feature request for VCL components: [email protected]
Important note:
All topics covered by this manual are officially supported and it’s unlikely that future versions will break backward compatibility. If this ever happens, all breaking changes will be covered in this manual and guidelines to update to a new version will be described. However, it’s important to note that parts of
TMS Aurelius code that are undocumented are not officially supported and are
subject to change, which includes breaking backward compatibility. In case you are using an unsupported/undocumented feature we will not provide support for upgrading and will not officially support it.
Breaking Changes
List of changes in each version that breaks backward compatibility from a previous version.
·
Merging transient objects with proxy collections was ignoring the collection content. TObjectManager.MergeListLegacyBehavior
·
Updating/Merging objects with proxied associations that were not modified was not clearing the value
·
Object manager now uses transactions by default. More info
Version 2.4
The process of
merging objects (Merge method) has improved, but this created
a breaking change. In previous versions, if you tried to merge an object without id, an exception would be raised. But if you tried to merge an object which had an association that pointed to an object with no id, nothing would happen and that association property would remain unchanged. It was an inconsistent behavior but no exception was raised. Starting from version 2.4, if you try to merge an object with no id, a copy of that instance will be saved. If it's an association, the instance will be replaced. This is a breaking change. For example, consider the following code:
Customer := TCustomer.Create;
Customer.Id := 1 ;
Country := TCountry.Create;
Country.Name := 'New Country' ;
Customer.Country := Country;
MergedCustomer := Manager.Merge<TCustomer>(Customer);
Customer has an id but Country has not. Customer will be merged and a different instance will be returned and put in MergedCustomer variable.
Previous to version 2.4, MergedCustomer.Country will point to the same
(c) 2016 TMS Software 17
TMS Aurelius Documentation
instance pointed by Country variable, and nothing would happen in database.
From version 2.4 and on, a copy of Country object will be saved in database, and MergedCustomer.Country will point to that new instance, which is different from the instanced referenced by Country variable. You should destroy the
Country instance.
Version 2.2
Packages were restructured to use LIBSUFIX, which means dcp (Delphi
Compiled Package) files won't have the a suffix indicating Delphi version. For example, in previous versions, the compiled package file for Delphi XE3 would be aureliusxe3.dcp. From version 2.2 and on, file name will be simply aurelius.dcp. Your application might be affected by this if you have packages that requires Aurelius packages. You will have you update your package files to require package "aurelius" instead of requiring package "aureliusxe3" (or whatever Delphi version you use). BPL files are unchanged, still keeping delphi version suffix (aureliusxe3.bpl).
1.6.1
Version 3.2 - Breaking Changes
Merging transient objects with proxy collections was ignoring the collection content.
This versions fixes a bug that might break existing code that was relying on such bug to work.
Suppose you have a list with a property using
lazy-loaded association (using
Proxy):
TCustomer =
class
{...}
FAddresses: Proxy<List<TAddress>>;
If you initialize such class and Merge it using an existing customer Id:
Customer := TCustomer.Create;
Customer.Id := 5 ;
Manager.Merge<TCustomer>(Customer);
Manager.Flush;
Expected behavior would be that all the existing Addresses associated with
Customer which Id=5 would be disassociated from it (or deleted if the association cascade included RemoveOrphan type.
However, for versions below 3.2, the property was being ignored when merging and the addresses were kept. So you must be sure that your code doesn't rely on such behavior, otherwise you might get some changes in data.
If you want to keep the old behavior, you can set a specific property in the object manager:
Manager.MergeListLegacyBehavior := True;
This will keep the old (and wrong) behavior.
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TMS Aurelius Documentation
Updating/Merging objects with proxied associations that were not modified was not clearing the value
On the other hand, suppose you have the same situation but with a single entity association:
TCustomer =
class
{...}
FCountry: Proxy<TCountry>;
If you create a new instance and update (or merge) it, leaving Country blank:
Customer := TCustomer.Create;
Customer.Id := 5 ;
Manager.Update(Customer);
// or
Manager.Merge<TCustomer>(Customer);
Manager.Flush;
Expected behavior would be that Country of customer with id = 5 in the database would be cleared.
However, for versions below 3.2, the value was being ignored and Country property was left unchanged. So be careful with the update because after updating existing code might behave differently (even though it was relying on a bug).
1.6.2
Version 2.9 - TObjectManager.UseTransactions
As of version 2.9, TObjectManager includes a property
. This property is true by default, meaning the behavior is different from previous versions. When true, the manager will create
for its internal operations (for example, when you call Save or Remove). This is to make sure that all SQL performed by the internal operations are executed successfully or all is reverted in case of error at any point.
In our (huge) test suite, we didn't detect any problem with backward compatibility, no regressions. But in any case you find an issue with version
2.9, please be aware of this change and consider if that can be the cause of the problem.
You can switch to previous behavior by setting that property to false, or globally using the
1.7
Online Resources
This topic lists some links to internet resources - videos, articles, blog posts about TMS Aurelius.
Official Online Documentation
(c) 2016 TMS Software 19
TMS Aurelius Documentation
"My Top 10 Aurelius Features" blog post and video series
Introduction (05-Dec-2016)
#10 - Automapping ( video link ) (05-Dec-2016)
#9 - Plain Old Delphi Objects ( video link ) (12-Dec-2016)
Malcolm Groves' series of articles "Storing your Objects in a Database" about TMS Aurelius (include videos):
Introduction (16-Jun-2016)
Getting Started (16-Jun-2016)
Extending the Model (11-Jul-2016)
Aurelius Crash Course (blog posts):
Getting Started
AnyDAC or dbExpress
Associations (Foreign Keys)
Using Blobs
Inheritance and Polymorphism
Visual Data Binding using TAureliusDataset
Conference/Webinar Videos
TMS Aurelius Free Edition - An Overview (CodeRage XI Session) (21-Nov-2016)
TMS Aurelius session at CodeRage 8 (download source code used in video)
Introducing TMS Aurelius, a Delphi ORM - Vendor Showcase
Portuguese Resources - Links em português
Vídeos em português:
TMS Aurelius - Usando TAureliusDataset
TMS Aurelius - Criando uma Aplicação
Grupo DCORM - reunião sobre TMS Aurelius/XData
TMS Aurelius e TMS XData - DCORM group meeting - 2014 (português)
(download source code )
TMS Aurelius e TMS XData - Embarcadero Conference 2013 (português)
(download source code ):
Curso Rápido TMS Aurelius (português)
Primeiros Passos
FireDac ou dbExpress?
Associações (Chaves Estrangeiras)
Artigos em Revistas
Artigo revista DevMedia - Mapeamento ORM com TMS Aurelius
(c) 2016 TMS Software 20
Chapter
II
Getting Started
TMS Aurelius Documentation
2 Getting Started
In this chapter we will provide you basic info about how to get started using
TMS Aurelius. They are simple examples, but shows you how quickly you can start use it, and how simple is that. The intention is to explain the macro structure of the framework and what are the major steps to setup it. For a full usage of the framework and full flexibility, see other chapters in this manual.
The following topics are covered in this chapter:
2.1
Quick Start
Here we describe minimal steps to get started using TMS Aurelius framework.
1. Create the class model
Create a new class to be saved in the database (you can also use an existing class in your application):
type
TPerson =
class private
FLastName:
string
;
FFirstName:
string
;
FEmail:
string
;
public property
LastName:
string read
FLastName
write
FLastName;
property
FirstName:
string read
FFirstName
write
FFirstName;
property
Email:
string read
FEmail
write
FEmail;
end
;
Your class can descend from any other Delphi class.
2. Define and map persistent entity class
Add
and
Automapping attributes to the class, and an integer FId field.
This will do
(All attributes you need are declared in unit Aurelius.Mapping.Attributes so you must add it to your unit)
uses
{...}
, Aurelius.Mapping.Attributes;
type
[Entity]
[Automapping]
TPerson =
class
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TMS Aurelius Documentation private
FId: integer;
FLastName:
string
;
FFirstName:
string
;
FEmail:
string
;
public property
Id: integer
read
FId;
property
LastName:
string read
FLastName
write
FLastName;
property
FirstName:
string read
FFirstName
write
FFirstName;
property
Email:
string read
FEmail
write
FEmail;
end
;
You can also fully customize
mapping - there is no need to use automatic one.
Even including an FId is not required if you don't use automatic mapping.
3. Obtain an
Get the component you use in your application to connect to the database
(dbExpress, ADO) and obtain an IDBConnection interface from it.
(The IDBConnection interface is declared in Aurelius.Drivers.Interfaces unit.
Each adapter is declared in a different unit, you must check which unit you must use for each
uses
{...}
, Aurelius.Drivers.Interfaces,
Aurelius.Drivers.dbExpress;
var
MyConnection: IDBConnection
begin
// SQLConnection1 is a dbExpress TSQLConnection component
// You can use several different data-access component libraries
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, false);
4. Specify the SQL dialect
Let Aurelius know which SQL dialects wlll be available to the application. You do that by adding a unit named Aurelius.SQL.XXX (where XXX is the name of
SQL dialect) to any unit of your application, or the project itself.
uses
{...}
, Aurelius.SQL.MySQL, Aurelius.SQL.MSSQL;
In the example above, we make Aurelius aware of MySQL and Microsoft SQL
Server dialects. The correct dialect will be chosen by Aurelius depending on the connection you specified in step 3. In that step (3) you can even specify which dialect you are using. There are plenty of
Aurelius.
(c) 2016 TMS Software 23
TMS Aurelius Documentation
5. Create the database
Use the
Database Manager to create the underlying database tables and fields
where the objects will be saved.
(TDatabaseManager is declared in unit Aurelius.Engine.DatabaseManager):
uses
{...}
, Aurelius.Engine.DatabaseManager;
DBManager := TDatabaseManager.Create(MyConnection);
DBManager.BuildDatabase;
If you have an existing database with specific fields and tables you want to use, just skip this step.
6. Instantiate and save objects
Now you can instantiate a new TPerson instance and save it in the database, using the
uses
{...}
, Aurelius.Engine.ObjectManager;
Person := TPerson.Create;
Person.LastName := 'Lennon' ;
Person.FirstName := 'John' ;
Person.Email := '[email protected]';
Manager := TObjectManager.Create(MyConnection);
try
Manager.Save(Person);
PersonId := Person.Id;
finally
Manager.Free;
end
;
A new record will be created in the database. Person.Id will be generated automatically.
7. Retrieve and update objects
Manager := TObjectManager.Create(MyConnection);
Person := Manager.Find<TPerson>(PersonId);
Person.Email := '[email protected]' ;
Manager.Flush;
Manager.Free;
This way you can retrieve object data, update values and save it back to the database
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TMS Aurelius Documentation
8. Perform queries
What if you want to retrieve all persons which e-mail belongs to domain
"beatles.org" or "beatles.com"?
(There are several units you can use to build queries. Aurelius.Criteria.Base
must be always used, then for filter expressions you can use
Aurelius.Criteria.Expression or Aurelius.Criteria.Linq if you prefer using linq-like operators. To use projections, use Aurelius.Criteria.Projections unit)
uses
{...}
, Aurelius.Criteria.Base, Aurelius.Criteria.Linq;
Manager := TObjectManager.Create(MyConnection);
Results := Manager.Find<TPerson>
.Where(
Linq[ 'Email' ].Like( '%beatles.org%' )
or
Linq[ 'Email' ].Like( '%beatles.com%' )
)
.List;
// Iterate through Results here, which is a TList<TPerson> list.
for
person
in
Results
do
// use person variable here, it's a TPerson object
Manager.Free;
9. What's Next?
With just the above steps you are able to create the database and SAVE your classes in there, being able to save, delete, update and query objects. But what if you want: a) Create a new class TCompany descending from TPerson and also save it?
Aurelius supports
inheritance strategies using the
b) Fine-tune the mapping to define names and types of the table columns where the class properties will be saved to?
You can do manual
mapping using several attributes like
and
define the database table and columns. You can even use
types to specify fields that can receive null values.
c) Create properties that are also objects or list of objects (e.g., a property
Country: TCountry in my TPerson class), and also save them?
You can do it, using
associations that can be fetched in a lazy or eager mode.
You do that using
attributes.
d) Define different identifier strategies, define sequences, unique indexes, etc., in my database?
Just use the several
e) Perform complex queries using different conditional expressions, grouping, ordering, aggregated functions, condition expression in associated objects, etc.?
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TMS Aurelius Documentation
Aurelius allow you to create complex
queries using all the mentioned features
and more, all at object-level. You don't need to use SQL statements for that.
f) Send/receive Aurelius objects in JSON format through REST servers or any other multi-tier architecture? You can build
with
Aurelius.
(c) 2016 TMS Software 26
Chapter
III
Database
Connectivity
TMS Aurelius Documentation
3
3.1
Database Connectivity
This chapter explains how you properly configure Aurelius to access the database where objects will be saved to. The following topics describe all ways you can connect to, which dialects are supported and even how to automatically create/destroy the database schema.
Components and Databases Homologation
Database Manager - Creating the Schema
Using the Connection Wizard
To connect to a database, you need an
IDBConnection interface representing
the database connection. The easiest way to get one is using the "TMS
Aurelius Connection" wizard which is available in Delphi IDE after you installed
Aurelius.
To create a new connection:
1. chose File > New > Other and then look for "TMS Business" category under "Delphi Projects". Then double click "TMS Aurelius Connection".
2. Select the Driver (
component to access database ) and the SQL Dialect
(
3. A new data module will be created with the component, configure the connection parameters and make sure it's connecting to the database.
4. To retrieve a new
from the data module, just use this code:
// The name of data module class might vary from
TFireDacMSSQLConnection
// depending on selected driver and SQL Dialect
NewConnection := TFireDacMSSQLConnection.CreateConnection;
Remarks
The wizard shows the following options:
Driver: Choose the database component you want to use to connect to the database. You can choose any that is supported by Aurelius
(c) 2016 TMS Software 28
TMS Aurelius Documentation
, like FireDac, dbExpress, dbGo (ADO), among others. "SQLite" is the native SQLite component adapter.
SQL Dialect: Choose the
SQL dialect to be used when executing SQL
statements to the database. Some drivers support several dialects (like FireDac for example), and some support just one (for example, SQLite driver only supports SQLite dialect).
You can freely configure and try the connection at design-time the usual way you do with your component, that's the purpose of it - to be RAD and working at design-time. It's always a good practice to close the connection once you have tested and configured it, though.
The name of the data module is automatically defined by the wizard and it's a combination of the driver and sql dialect you selected. In the example above, it was FireDac driver and MSSQL dialect, but could be different. You can always change this name later.
It's important to note that no instance of the data module will be autocreated. Also, the CreateConnection method always create a new instance of the data module, so if you intend to use a single global connection for the application (which is usual for client/server applications), call CreateConnection just once and save the created IDBConnection interface for further use.
3.2
IDBConnection Interface
The IDBConnection interface represents a connection to a database in Aurelius.
Every object that needs to connect to a database just uses this interface to send and receive data from/to the database. As an example, when you create a
object, you need to pass a IDBConnection interface to it so it can connect to the database.
IDBConnection wraps the data access component you are using, making it transparent for the framework. Thus, regardless if you connect to the database using dbExpress, ADO, IBX, etc., you just need IDBConnection.
To obtain an IDBConnection interface you use the adapters in Aurelius. The adapters just take an existing data access component (TSQLConnection,
TADOConnection, etc.) and give you back the IDBConnection interface you need to use. To create database connections it's important to know the available:
In summary:
To obtain an IDBConnection interface
1. Create and configure (or even use an existing one) component that makes a connection to your database
(c) 2016 TMS Software 29
TMS Aurelius Documentation
If you use dbExpress, for example, just drop a TSQLConnection component on the form and configure it. Or you can just use the existing one you have in your application. Suppose this component is named SQLConnection1.
SQLConnection1: TSQLConnection;
2. Instantiate an adapter passing the connection component var
MyConnection: IDBConnection;
begin
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, False);
// Use your connection now
Manager := TObjectManager.Create(MyConnection);
...
end
;
For more information about how to create adapters, see
.
3.3
Component Adapters
There is an adapter for each data-access component. For dbExpress, for example, you have TDBExpressConnectionAdapter, which is declared in unit
Aurelius.Drivers.dbExpress. All adapters are declared in unit Aurelius.Drivers.XXX
where XXX is the name of data-access technology you're using. You can create your own adapter by implementing IDBConnection interfaces, but
Aurelius already has the following adapters available:
Technolog y
Absolute
Database
Adapter class Declared in unit
TAbsoluteDBConn ectionAdapter
Aurelius.Drive
rs.AbsoluteDB
AnyDac TAnyDacConnecti onAdapter
Aurelius.Drive
rs.AnyDac
dbExpress TDBExpressConne ctionAdapter
Aurelius.Drive
rs.dbExpress
dbGo (ADO) TDbGoConnection
Adapter
Aurelius.Drive
rs.dbGo
Direct
Oracle
Access
(DOA)
TDoaConnectionA dapter
Aurelius.Drive
rs.Doa
Adapted
Compone nt
TABSData base
TADDatab ase
TSQLConn ection
TADOConn ection
TOracleSe ssion
Vendor Site
http:// www.componentace.
com http://www.dasoft.com/anydac
Delphi Native
Delphi Native http:// www.allroundautoma
tions.com
ElevateDB TElevateDBConne ctionAdapter
Aurelius.Drive
rs.ElevateDB
TEDBData base http:// elevatesoftware.com
/
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TMS Aurelius Documentation
Technolog y
Adapter class Declared in unit
Adapted
Compone nt
Vendor Site
FIBPlus
FireDac
IBObjects
(IBO)
Interbase
Express
(IBX)
TFIBPlusConnecti onAdapter
Aurelius.Drive
rs.FIBPlus
TFireDacConnecti onAdapter
Aurelius.Drive
rs.FireDac
TIBObjectsConne ctionAdapter
TIBExpressConne ctionAdapter
Aurelius.Drive
rs.IBObjects
Aurelius.Drive
rs.IBExpress
TFIBDatab ase
TFDConne ction http:// www.devrace.com/
Delphi native
TIBODatab ase http:// www.ibobjects.com/
TIBDataba se
Delphi Native
NexusDB TNexusDBConnec tionAdapter
SQL-Direct TSQLDirectConne ctionAdapter
SQLite
UniDac
TSQLiteNativeCo nnectionAdapter
TUniDacConnecti onAdapter
Aurelius.Drive
rs.NexusDB
Aurelius.Drive
rs.SqlDirect
Aurelius.Drive
rs.SQLite
Aurelius.Drive
rs.UniDac
TnxDataba se http:// www.nexusdb.com
TSDDatab ase http:// www.sqldirectsoft.com
(not applicable)
TMS Aurelius Native
TUniConne ction http:// www.devart.com/ unidac
Unified
Interbase
(UIB)
TMS
RemoteDB
Server
ZeosLib
TUIBConnectionA dapter
TRemoteDBConne ctionAdapter
Aurelius.Drive
rs.RemoteDB
TZeosLibConnecti onAdapter
Aurelius.Drive
rs.UIB
Aurelius.Drive
rs.ZeosLib
TUIBDatab ase http:// sourceforge.net/ projects/uib/
TRemoteD
BDatabase http:// www.tmssoftware.co
m/site/remotedb.asp
TZConnec tion https:// sourceforge.net/ projects/zeoslib
Creating the adapter
To create the adapter, you just need to instantiate it, passing an instance of the component to be adapted. In the example below, a dbExpress adapter constructor receives a TSQLConnection component.
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, False);
The adapter usually detects the
SQL Dialect automatically, but you can force
the adapter to use a specific dialect, using one of the following overloaded constructors
Overloaded constructors
There are some overloaded versions of the constructor for all adapters:
(c) 2016 TMS Software 31
TMS Aurelius Documentation constructor
Create(AConnection: T; AOwnsConnection: boolean);
overload
;
virtual
;
constructor
Create(AConnection: T; ASQLDialect:
string
;
AOwnsConnection: boolean);
overload
;
virtual
;
constructor
Create(AConnection: T; OwnedComponent: TComponent);
overload
;
virtual
;
constructor
Create(AConnection: T; ASQLDialect:
string
;
OwnedComponent: TComponent);
overload
;
virtual
;
AConnection: specify the database-access component to be adapted.
AOwnsConnection: if true, the component specified in AConnection parameter will be destroyed when the IDBConnection interface is released. If false, the component will stay in memory.
ASQLDialect: defines the SQL dialect to use when using this connection. If not specified, Aurelius will try to discover the SQL Dialect based on the settings in the component being adapted.
OwnedComponent: specifies the component to be destroyed when the
IDBConnection interface is released. This is useful when using data modules
(see below).
Memory Management
Note the second boolean parameter in the Create constructor of the adapter.
It indicates if the underlying connection component will be destroyed when the
IDBConnection interface is destroyed. In the example above ("Creating the adapter"), the SQLConnection1 component will remain in memory, even after
MyConnection interface is out of scope and released. If you want the component to be destroyed, just pass the second parameter as true. You will usually use this option when you create a connection component just for
Aurelius usage. If you are using an existing component from your application, use false. Quick examples below:
var
MyConnection: IDBConnection;
begin
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, False);
// ...
MyConnection :=
nil
;
{ MyConection is nil, the TDBExpressConnectionAdapter component is destroyed,
but SQLconnection1 component remains in memory}
end
;
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MyConnection: IDBConnection;
SQLConnection1: TSQLConnection;
begin
SQLConnection1 := TSQLConnection.Create(
nil
);
// Set SQLConnection1 properties here in code
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, True);
// ...
MyConnection :=
nil
;
{ MyConection is nil, the TDBExpressConnectionAdapter component is destroyed,
and SQLConnection1 is also destroyed }
end
;
Alternatively, you can inform a component to be destroyed when the interface is released. This is useful when you want to create an instance of a
TDataModule (or TForm) and use an adapted component that is owned by it.
For example:
MyDataModule := TConnectionDataModule.Create(
nil
);
MyConnection :=
TDBExpressConnectionAdapter.Create(MyDataModule.SQLConnection1,
MyDataModule);
The previous code will create a new instance of data module
TConnectionDataModule, then create a IDBConnection by adapting the
SQLConnection1 component that is in the data module. When MyConnection is released, the data module (MyDataModule) will be destroyed. This is useful if you want to setup the connection settings at design-time, but want to reuse many instances of the data module in different connections (for multi-threading purposes, for example).
Referencing original component
All component adapters provide a Connection property that references back the original component passed to constructor. This is useful if you need to retrieve that instance from an existing IDBConnection interface if you know the original adapter used. For example, given an IDBConnection that you know was created from a TFireDacConnectionAdapter, you can retrieve the
TFDConnection object using the following code:
var
MyConnection: IDBConnection;
FDConnection: TFDConnection;
{...}
FDConnection := (MyConnection
as
TFireDacConnectionAdapter).Connection;
Native SQLite Adapter
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Aurelius provides native SQLite database adapter. You just need to have sqlite3.dll in a path Windows/Mac can find. Creating SQLite adapter is a little different than other adapters, since you don't need to pass a component to be adapter. With the SQLite adapter, you just pass the name of the database file to be open (or created if it doesn't exist):
MySQLiteConnection := TSQLiteNativeConnectionAdapter.Create( 'C:
\Database\SQLite\MyDatabase.sdb' );
TSQLiteNativeConnectionAdapter class also has two additional methods that you can use to manually disable or enable foreign keys in SQLite (foreign keys are enforced at connection level, not database level in SQLite!).
procedure
EnableForeignKeys;
procedure
DisableForeignKeys;
So if you want to use SQLite with foreign keys, do this to retrieve your connection:
var
SQLiteAdapter: TSQLiteNativeConnectionAdapter;
MySQLiteConnection: IDBConnection;
begin
SQLiteAdapter := TSQLiteNativeConnectionAdapter.Create( 'C:
\Database\SQLite\MyDatabase.sdb' );
SQLiteAdapter.EnableForeignKeys;
MySQLiteConnection := SQLiteAdapter;
// Use MySQLiteConnection interface from now on
dbGo (ADO) Adapter
Currently dbGo (ADO) is only officially supported when connecting to Microsoft
SQL Server databases. Drivers for other databases might work but were not tested.
3.4
SQL Dialects
To save and manipulate objects in the database, TMS Aurelius internally build and execute SQL statements. The SQL statements are automatically adjusted to use the correct dialect, according to the database server being used by the programmer.
When you create an
IDBConnection interface using a
usually the adapter will automatically specify to Aurelius the SQL dialect to use. For example, if you are using dbExpress components, the adapter will look to the DriverName property and tell which db server you are using, and then define the correct SQL dialect name that should be used.
However, the SQL dialect must be explicity registered in the global settings for
Aurelius. This is by design so you don't need to load units for SQL dialects you won't use. To register an SQL dialect, just use a unit named Aurelius.SQL.XXX
where XXX is the name of the SQL dialect. The following table lists all current
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3.5
SQL dialects supported, the exact string identifier, and the unit you must add to your project in order for the dialect to be registered.
SQL dialect
Absolute
Database
DB2
ElevateDB
Firebird
Firebird3 (*)
Interbase
Microsoft SQL
Server
MySQL
NexusDB
Oracle
PostgreSQL
SQLite
String identifier
Declared in unit Database Web Site
AbsoluteDB Aurelius.Sql.Absol
uteDB http:// www.componentace.com
DB2 Aurelius.Sql.DB2
http://www.ibm.com
ElevateDB Aurelius.Sql.Eleva
teDB http:// www.elevatesoftware.com
Firebird
Firebird3
Interbase
MSSQL
MySQL
Aurelius.Sql.Firebi
rd http://www.firebirdsql.org
Aurelius.Sql.Firebi
rd3 http://www.firebirdsql.org
Aurelius.Sql.Inter
base http:// www.embarcadero.com
Aurelius.Sql.MSS
QL
Aurelius.Sql.MyS
ql http://www.microsoft.com/ sqlserver http://www.mysql.com
NexusDB
Oracle
Aurelius.Sql.Nexu
sDB http://www.nexusdb.com
Aurelius.Sql.Oracl
e http://www.oracle.com
PostgreSQL Aurelius.Sql.Post
greSQL
SQLite Aurelius.Sql.SQLit
e http://www.postgresql.org
http://www.sqlite.org
Note that in some situations, the adapter is not able to identify the correct dialect. It can happen, for example, when you are using ODBC or just another data access component in which is not possible to tell which database server the component is trying to access. In this case, when creating the adapter, you can use an overloaded constructor that allows you to specify the SQL dialect to use:
MyConnection :=
TDBExpressConnectionAdapter.Create(SQLConnection1, 'MSSQL' ,
False);
(*) The difference between Firebird and Firebird3 is that the latter uses boolean fields and identity fields by default. Please check
Dialects for more details on how to configure specific SQL dialects.
Configuring SQL Dialects
Some
SQL Dialects have configuration options that you can use to fine tune
how they work. For that you need to retrieve the original SQL Dialect object
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and then change specific properties. This is the pattern you use to retrieve a generator:
uses
Aurelius.Sql.
Register
, Aurelius.Sql.Firebird;
var
Generator: TFirebirdSQLGenerator;
begin
Generator :=
(TSQLGeneratorRegister.GetInstance.GetGenerator( 'Firebird' )
as
TFirebirdSQLGenerator);
// Set Generator properties
end
;
For other dialects, you can just replace "Firebird" occurrences by the name of the different dialect. The following sections show the dialects that have properties you can configure:
MSSQL (Microsoft SQL Server)
Sample:
uses
Aurelius.Sql.
Register
, Aurelius.Sql.MSSQL;
{...}
(TSQLGeneratorRegister.GetInstance.GetGenerator( 'MSSQL' ) as
TMSSQLSQLGenerator).UseBoolean := True;
Properties
Name
property
UseBoolean:
Boolean
Description
Specifies how boolean values will be represented in database. If False (default), then booleans will be represented by CHAR(1) type. If True, booleans will be represented by BIT type.
Firebird3 (Firebird 3.x)
Sample:
uses
Aurelius.Sql.
Register
, Aurelius.Sql.Firebird3;
{...}
(TSQLGeneratorRegister.GetInstance.GetGenerator( 'Firebird3' ) as
TFirebird3SQLGenerator).UseBoolean := False;
(TSQLGeneratorRegister.GetInstance.GetGenerator( 'Firebird3' ) as
TFirebird3SQLGenerator).UseIdentity := False;
The code above makes the Firebird3 dialect to behave like the regular Firebird dialect (which is targeted at Firebird 2.x).
Properties
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Name
property
UseBoolean:
Boolean property
UseIdentity:
Boolean
Description
Specifies how boolean values will be represented in database. If False, then booleans will be represented by
CHAR(1) type. If True, booleans will be represented by
BOOLEAN type. Default is True.
Specifies how
generators of type
SequenceOrIdentity will behave. If False, then
Sequences will be used. If True, Identity fields will be used. Default is True.
3.6
Schema Importers
To be able to
validate database schema , Aurelius needs to perform
reverse engineering in the database. This is accomplished by using schema importers that execute specific SQL statements to retrieve the database schema, depending on the database server being used. To find the correct importer, Aurelius searches for a list of registered schema importers, using the same
SQL Dialect used by the current connection. So, for example, if the
current SQL Dialect is "MySQL", Aurelius will try to find a schema importer named "MySQL".
By default, no schema importers are registered. You must be explicity register a schema importer in the global settings for Aurelius. This is by design so you don't need to load units for schema importers you won't use. To register an schema importer, just use a unit named Aurelius.Schema.XXX where XXX is the name of the SQL dialect associated with the schema importer. The following table lists all current schema importers supported, the exact string identifier, and the unit you must add to your project in order for the dialect to be registered.
Schema Importer for String identifier
(associated SQL
Dialect
Absolute Database AbsoluteDB
DB2
ElevateDB
Firebird
DB2
ElevateDB
Firebird
Interbase Interbase
Microsoft SQL Server MSSQL
MySQL
NexusDB
Oracle
MySQL
NexusDB
Oracle
PostgreSQL
SQLite
PostgreSQL
SQLite
Declared in unit
Aurelius.Schema.AbsoluteDB
Aurelius.Schema.DB2
Aurelius.Schema.ElevateDB
Aurelius.Schema.Firebird
Aurelius.Schema.Interbase
Aurelius.Schema.MSSQL
Aurelius.Schema.MySql
Aurelius.Schema.NexusDB
Aurelius.Schema.Oracle
Aurelius.Schema.PostgreSQL
Aurelius.Schema.SQLite
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3.7
Components and Databases Homologation
The following table presents which data-access component can be used to access each relational database server. Note that some components can access more databases than what's described here (especially dbGo (ADO) which can access several databases through OleDB drivers). However, the table below shows what has been tested and is officially supported by TMS
Aurelius.
Interb ase
MS
SQL
Serve r
MySQ
L
Nexus
DB
Oracl e
Postg reSQL
SQLit e
Absol uteDB
DB2
Eleva teDB
Firebir d
Nati ve
Abs olut e x x
Any
Dac dbEx press db
Go
D
O
A
Eleva teDB
Fire
Dac
FIB
Plus
IB
O
IB
X
Nex us
SQL
Direc t
Uni
Dac x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x
UI
B
Ze os
Lib x x x x x x
Database versions used for homologation are listed below. TMS Aurelius tries to use no syntax or features of an specific version, its internal code uses the most generic approach as possible. Thus, other versions will most likely work, especially newer ones, but the list below is provided for your reference.
Database
AbsoluteDB
DB2
ElevateDB
Version
7.05
9.7.500
2.08
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Firebird
Interbase
MS SQL Server
MySQL
NexusDB
Oracle
PostgreSQL
SQLite
2.5.1
XE (10.0.3)
2008 R2 (10.50.1600)
5.5.17 (Server)
5.1.60 (Client)
3.0900
10g Express
(10.2.0.1.0)
9.1
3.7.9
Analog to databases above, in table below we list data-access components used for homologation and respective versions. Newer versions should work with not problems.
Component Library
AbsoluteDB
AnyDac dbExpress dbGo
Direct Oracle Access
ElevateDB
Versions
7.05
5.0.3.1917
16.0
Delphi 2010 up to XE3
4.1.3.3
2.08
FIBPlus
FireDac
IBObjects
IBX
NexusDB
7.2
Delphi XE5 and up
4.9.14
Delphi 2010 up to XE2
3.0900, 3.1003
SQL-Direct
UniDac
6.3
4.1.4
4.1.5 (for NexusDB)
Unified Interbase (UIB) 2.5 revision 428
(01-Feb-2013)
ZeosLib 7.3
3.8
Database Manager - Creating/Updating Schema
If you have an existing database, you can use Aurelius on it. You can map your existing or new classes to the tables and fields of existing databases, and that's it. But for new applications, you might consider just modeling the classes, and let Aurelius build/update the database structure for you, creating all database objects needed to persist the objects. To do that, just create a
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TDatabaseManager object (declared in unit Aurelius.Engine.DatabaseManager) the same way you create a
TObjectManager , and use one of the methods
available to manager the schema (database structure). Common usage is as following:
uses
Aurelius.Engine.DatabaseManager;
{...}
var
DBManager: TDatabaseManager;
begin
DBManager := TDatabaseManager.Create(MyConnection);
// use default mapping explorer
// operate on database schema using DBManager
DBManager.Free;
end
; alternatively, you can also pass a
, which holds a custom
.
DBManager := TDatabaseManager.Create(MyConnection,
MyMappingExplorer);
The following topics explain how to use the database manager object.
3.8.1
Creating New Schema
You can create a new schema from an empty database using method
BuildDatabase:
uses
Aurelius.Engine.DatabaseManager;
{...}
var
DBManager: TDatabaseManager;
begin
DBManager := TDatabaseManager.Create(MyConnection);
DBManager.BuildDatabase;
DBManager.Free;
end
;
This method will execute all SQL statements that create the whole database structure needed to persist the
. It does not take into
account the existing database schema, so if tables already exist, an "object already exists" error will happen in database server when executing the statement. You can alternatively just
without executing it.
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Even though this method does not perform any reverse engineering to check existing database structure, a
schema validation result is available. Results are
provided as if the existing database is empty.
3.8.2
Updating Existing Schema
You can update the existing database structure using method
UpdateDatabase:
uses
Aurelius.Engine.DatabaseManager;
{...}
var
DBManager: TDatabaseManager;
begin
DBManager := TDatabaseManager.Create(MyConnection);
DBManager.UpdateDatabase;
DBManager.Free;
end
;
This method will:
1. Perform a
schema validation , which consists of:
a) Execute SQL statements to perform a reverse engineering in the database, retrieving the existing database schema (*).
b) Compare the existing schema with the target schema (all database objects table, columns, etc. - need to persist the
c) Provide info about the differences between the two schema (see
schema validation for details).
d)
needed to update the database schema
2. Execute the SQL Script in the database, unless command execution is disabled (see
(*) Note: for Aurelius to properly import database schema, you need to register a schema importer according to the database server you are connecting to. For example, to import MySQL schema, just use the unit
"Aurelius.Schema.MySQL" anywhere in your project.
If
command execution is disabled , this method behaves exactly as the
Since this method performs on a database that has existing object and data, it has some limitations. First, if you are unsure of the effects of schema update, it's strongly recommended that you check
results before updating. Errors might occur when updating the schema, for example, if new schema requires a foreign key creating but existing data doesn't fit into this new constraint. See
schema validation for a list of current valid operations and
limitations.
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Note that UpdateDatabase is a non-destructive method. This means that even if the validation reports that a data-holding object (table or column) needs to be dropped, the SQL statement for it will not be performed.
3.8.3
Dropping Existing Schema
You can drop the whole database structure from an existing database using method DestroyDatabase:
uses
Aurelius.Engine.DatabaseManager;
{...}
var
DBManager: TDatabaseManager;
begin
DBManager := TDatabaseManager.Create(MyConnection);
DBManager.DestroyDatabase;
DBManager.Free;
end
;
This method will execute all SQL statements that destroy the whole database structure needed to persist the
. It does not take into
account the existing database schema, so if tables were already dropped, an
"object does not exist" error will happen in database server when executing the statement. You can alternatively just
without executing it.
Even though this method does not perform any reverse engineering to check existing database structure, a
schema validation result is available. Results are
provided as if the existing database is complete, with all objects, and target database structure is empty.
3.8.4
Schema Validation
Schema validation is a process that gives you the differences between the existing database schema and the needed schema to make the current application to work. You can validate the existing database structure using method ValidateDatabase. The method returns true if there are no differences in that comparison (meaning that the existing database structure has all database objects needed by the application):
uses
Aurelius.Engine.DatabaseManager,
Aurelius.Schema.Messages;
{...}
var
DBManager: TDatabaseManager;
SchemaMessage: TSchemaMessage;
begin
DBManager := TDatabaseManager.Create(MyConnection);
if
DBManager.ValidateDatabase
then
WriteLn( 'Database strucuture is valid.' )
else begin
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WriteLn(Format( 'Invalid database structure. %d Errors, %d
Warnings, %d Actions' ,
[DBManager.ErrorCount, DBManager.WarningCount,
DBManager.ActionCount]));
for
SchemaMessage
in
DBManager.Warnings
do
WriteLn( 'Warning: ' + SchemaMessage.Text);
for
SchemaMessage
in
DBManager.Errors
do
WriteLn( 'Error: ' + SchemaMessage.Text);
for
SchemaMessage
in
DBManager.Actions
do
WriteLn( 'Action: ' + SchemaMessage.Text);
end
;
DBManager.Free;
end
;
This method will: a) Execute SQL statements to perform a reverse engineering in the database, retrieving the existing database schema (*). b) Compare the existing schema with the target schema (all database objects table, columns, etc. - need to persist the
c) Provide info about the differences between the two schema (see
schema validation for details).
d)
needed to update the database schema
(*) Note: for Aurelius to properly import database schema, you need to register a schema importer according to the database server you are connecting to. For example, to import MySQL schema, just use the unit
"Aurelius.Schema.MySQL" anywhere in your project.
If
command execution is disabled , this method behaves exactly as the
method.
The comparison result is provided through properties Actions, Warnings and
Errors and also ActionCount, WarningCount and ErrorCount, defined as following:
property
Actions: TEnumerable<TSchemaAction>;
property
Warnings: TEnumerable<TSchemaWarning>;
property
Errors: TEnumerable<TSchemaError>;
property
ActionCount: integer;
property
WarningCount: integer;
property
ErrorCount: integer;
TSchemaAction, TSchemaWarning and TSchemaError classes inherit from
TSchemaMessage class, which just has a public Text property with the information about the difference. The concept of each message type (actio, warning, error) is described as follows:
Actions
Actions are reported differences between the two schemas which associated
SQL update statements can be safely executed by the database manager.
Examples of differences that generate actions:
·
A new table
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·
A new nullable column in an existing table
·
A new sequence
·
A new non-unique index (
·
Foreign key removal (if supported by database)
·
Unique key removal (if supported by database)
Warnings
Warnings are reported differences between the two schemas which associated
SQL update statements can be executed by the database manager, but it
might cause runtime errors depending on the existing database data.
Examples of differences that generate actions:
·
A new not null column in an existing table (to be safe, when updating existing schema, try to always create new columns as nullable)
·
A new foreign key (usually you will create a new association, which will generate actions for new foreign key and new columns, which will not cause problem, unless the association is required. It's a warning if supported by database)
Errors
Errors are reported differences between the two schemas which associated
SQL update statements cannot be executed by the database manager. This means that updating the schema will not make those differences disappear, and you would have to change the schema manually. The fact it is reported as
"Error" does not mean the application will not work. It just means that the manager cannot update such differences. Examples of differences that generate errors:
·
Column data type change
·
Column Null/Not Null constraint change
·
Column length, precision or scale change
·
A new foreign key (if database does not support such statement)
·
Foreign key removal (if database does not support such statement)
·
Unique key removal (if database does not support such statement)
·
Changes in primary key (id fields)
·
Column removal
·
Table removal
·
Sequence removal
·
A new unique key
Schema comparison options
You can use some properties to define how Aurelius will detect changes in existing schema.
Properties
Name
property
IgnoreConstraintNa me: Boolean
Description
When False, the validator will compare constraints
(foreign key and unique key) by their name. If the name is different, they are considered different keys. This is
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the default for all databases except SQLite. When True, the validator will analyze the content of the foreign key, regardless the name. For example, if the foreign keys relates the same two tables, using the same fields, it's considered to be the same foreign key. You can set this option to True if you have created your database using a different tool than Aurelius, thus the foreign keys might have different names but you don't want Aurelius to recreated them.
3.8.5
Generating SQL Script
All TDatabaseManager methods that perform some operation in the database schema generate an SQL script, available in the SQLStatements property.
Most methods also execute such statements (like
and
DropDatabase ). Some methods do not execute, like
ValidateDatabase . But in all cases, the associated SQL script is available.
In TDatabaseManager you have the option to disable execution of SQL statements. This way you have the freedom to execute the statements as you want, using you our error handling system, your own graphical user interface to execute them, etc. To do that, just set SQLExecutionEnabled property to
false. Examples:
uses
Aurelius.Engine.DatabaseManager;
{...}
var
DBManager: TDatabaseManager;
procedure
OutputSQLScript;
var
SQLStatement:
string
;
begin for
SQLStatement
in
DBManager.SQLStatements
do
WriteLn(SQLStatement);
end
;
begin
DBManager := TDatabaseManager.Create(MyConnection);
DBManager.SQLExecutionEnabled := false;
// Output an SQL Script to build a new database
DBManager.BuildDatabase;
OutputSQLScript;
// Output an SQL to drop the full database
DBManager.DropDatabase;
OutputSQLScript;
// Output an SQL script to update the existing database
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DBManager.UpdateDatabase;
OutputSQLScript;
DBManager.Free;
end
;
Note that when SQLExecutionEnabled property is false, calling UpdateDatabase is equivalent to calling ValidateDatabase, so this code:
// Output an SQL script to update the existing database
DBManager.SQLExecutionEnabled := false;
DBManager.UpdateDatabase;
OutputSQLScript;
Could also be written just as:
// Output an SQL script to update the existing database
// Regardless of value of SQLExecutionEnabled property
DBManager.ValidateDatabase;
OutputSQLScript;
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Chapter
IV
Mapping
TMS Aurelius Documentation
4 Mapping
This chapter provides you information about how to map your classes to the database. While a mapping can be made so simple using a single
attribute, it can be fully configurable and might need lots of concepts to be done the way you need. Several mapping
attributes are available, you can also
create your classes using special types like
Nullable<T> and TBlob, and so on.
The topics below describe all the mapping mechanism in TMS Aurelius.
4.1
Attributes
Object-Relational Mapping in Aurelius is done by using attributes. With this approach you can do your mapping directly when coding the classes, and by browsing the source code you can easily tell how the class is being mapped to the database.
Basically you just add attributes to the class itself, or to a field or property:
[Table( 'Customer' )]
TMyCustomer =
class private
[Column( 'Customer_Name' )]
FCustomerName:
string
;
...
For column and associations mapping Aurelius accepts mapping attributes in either class field or class property (but not both of course). We recommend using mapping attributes in fields whenever it's possible, for several reasons:
1. Attributes are kept in private section of your class, leaving the public section clean and easily readable
2. Fields represent better the current state of the object. Properties can have getter and setters based on other data that it's not exactly the object state for persistance.
3. Some Aurelius features are better suited for fields. For example, lazy-loaded associations requires the use of a Proxy type, which makes more sense to be uses in fields (although you can use it in properties)
Still, there are situations where creating mapping attributes in properties are interesting, when for example you want to save the result of a runtime calculation in database.
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Available attributes (declared in unit Aurelius.Mapping.Attributes):
Basic Mapping
Association Mapping
Many-Valued Association Mapping
Inheritance Mapping
Automapping
Concurrency Control
Other attributes
4.1.1
Entity
Indicates that the class is an entity class, which means it can be persisted.
Level: Class Attribute
Description
Every class that you want to be persisted in database must have this attribute. It's also used by Aurelius for automatic class registration. When automatic registration is active in
, every class marked with
Entity attribute will be automatically registered as an entity class.
Constructor constructor
Create;
Parametes
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None.
Usage
[Entity]
TCustomer =
class
(TObject)
4.1.2
Id
Specify the Identifier of the class.
Level: Class Attribute
Description
Every object must be uniquely identified by Aurelius so that it can properly save and manage it. The concept is similar to a primary key in database. This attribute allows you to specify which field (or property) in the class will be used to uniquely identify the class. The value of that field/property must be unique for every object, and you can specify how that value will be generated for each object.
In addition, if you are creating the database structure from the mapped classes, Aurelius will create a primary key in the database corresponding to the field/column mapping.
If you are using inheritance, you must only declare the Id attribute in the base class of the hierarchy (the ancestor class). The inherited child classes can't have their own Id attribute.
For
composite id's , specify as many Id attributes as you need to build the
composite identifier.
Constructor constructor
Create(AMemberName:
string
; AGenerator:
TIdGenerator);
Parameters
AMemberN
Contains the name of field or property that identifies the object
ame
AGenerato
Indicates how the Id value will be generated. Valid values are
r
(prefixed by TIdGenerator):
None Id value will not be automatically generated. Your application must assign a value to it and be sure it's unique
IdentityOrSe quence
Aurelius will ask the database to generate a new Id. If the database supports sequences and a sequence is defined, then Aurelius will use the sequence to generate the value. Otherwise, it will use identity
(auto-numerated) fields. If no sequence is defined and database doesn't support identity fields, an exception will be raised. The name of the sequence to be created and used by Aurelius can be defined using the
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Guid
Uuid38
Uuid36
Sequence attribute. The type of the property that
identifies the entity should be integer.
Aurelius will generate a GUID (Globally Unique
Identifier) value as the entity identifier. The type of the property that identifies the entity should be TGuid or string.
Aurelius will generate a 38-length UUID (Universally
Unique Identifier) value as the entity identifier. An
UUID is just a string representation of a GUID value, with the format "{550e8400-e29b-41d4-a716-
446655440000}" (with hifens and curly brackets). The type of the property that identifies the entity should be string (with a minimum length of 38 characters)
Aurelius will generate a 36-length UUID (Universally
Unique Identifier) value as the entity identifier. An
UUID is just a string representation of a GUID value, with the format "550e8400-e29b-41d4-a716-
446655440000" (with hifens but no curly brackets).
The type of the property that identifies the entity should be string (with a minimum length of 36 characters)
Uuid32 Aurelius will generate a 32-length UUID (Universally
Unique Identifier) value as the entity identifier. An
UUID is just a string representation of a GUID value, with the format
"550e8400e29b41d4a716446655440000" (no hifens and no curly brackets). The type of the property that identifies the entity should be string (with a minimum length of 32 characters)
SmartGuid Aurelius will generate a sequential GUID (Globally
Unique Identifier) value optimized for the database being used. The generated sequential GUID will minimize clustered index fragmentation, which is an usual problem when using regular GUID's, causing performance loss. Aurelius will choose the best algorithm to generate the GUID sequence depending on the database being used. For most of them, the GUID will be sequential in its string format, which is optimum for most databases and also when you use string properties. For Microsoft SQL Server, for example, it will choose a different algorithm (sequential in the last bytes) which is best given the way SQL Server sorts
GUID's internally. In general you should use SmartGuid generator instead of Guid since both achieve the same results but SmartGuid performs better.
For
composite id's this value is ignored and None is used.
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Usage
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TCustomer =
class
(TObject)
private
[Column( 'CUSTOMER_ID' )]
FId: integer;
4.1.3
Table
Specify the database table where the objects will be saved to.
Level: Class Attribute
Description
Use the Table attribute to map the class to a database table. Every object instance saved will be a record in that table.
If you are using inheritance with
single table strategy , you must use the Table
attribute in the ancestor class only, since all classes will be saved in the same table.
If you are using inheritance with
, you must use Table attribute in all classes, since every class will be saved in a different table.
Constructor constructor
Create(Name:
string
);
overload
;
constructor
Create(Name, Schema:
string
);
overload
;
Parameters
Name
The name of the table in database
Schema
Optionally you can specify the schema of the database
Usage
[Table( 'Customers' )]
TCustomer =
class
(TObject)
private
[Table( 'Orders' , 'dbo' )]
TOrder =
class
(TObject)
private
4.1.4
Column
Specify the table column where the field/property value will be saved to.
Level: Field/Property Attribute
Description
Use Column attribute to map a field/property to a table column in the database. When saving an object, Aurelius will save and load the field/property value in the specified table column. Only fields/properties mapped using a
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Column attribute will be saved in the database (unless class is automapped using
Aurelius will define the table column data type automatically based on type of field/property being mapped.
Constructor constructor
Create(Name:
string
);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps;
Length: Integer);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps;
Precision, Scale: Integer);
overload
;
Parameters
Name
Properties
Contains the name of table column in the database where the field/property will be mapped to
A set containing zero or more options for the column.
TColumnProps and TColumnProp are declared as follow:
TColumnProp = (Unique, Required, NoInsert,
NoUpdate);
TColumnProps =
set of
TColumnProp;
Unique Values of this column must be unique. Aurelius will create an unique key (index) in the database to ensure unique values for this column. The index name will be the same as the column name. If you want to define a different name, do not set this flag and use
Required Column must be NOT NULL. Values are required for this field/property
NoInsert When inserting a record in the database, do not include this column in the INSERT command. The value of this field/property will not be saved in the database in INSERT commands. Note that for
using identity (autogenerated), Aurelius will automatically not include the field in the INSERT statement, regardless if cpNoInsert is specified or not
NoUpdate When updating a record in the database, do not include this column in the UPDATE command. The value of this field/property will not be saved in the database in UPDATE commands. This flag is usually used for Id fields which once inserted should not be changed anymore
Lazy Used for
blob fields only. Indicates that
will be used for the blob, i.e., the content of the blob will only be retrieved from the database when needed.
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Length
Precision,
Scale
If the property is not of type
ignored.
Used for string field/property. It's the maximum length of the table column. Usually this is mapped to the VARCHAR type, i.e., if Length is 30, the data type of table column will be
VARCHAR(30). It it's not specified, Aurelius will use the default length for string data types.
Used for numeric field/property. Specifies the precision and scale of numeric columns in the database table. If not specified, default values will be used.
Usage
[Column( 'MEDIA_NAME' , [TColumnProp.Required], 100 )]
property
MediaName:
string read
FMediaName
write
FMediaName;
[Column( 'DURATION' , [])]
property
Duration: Nullable<integer>
read
FDuration
write
FDuration;
4.1.5
Model
Specify the
model where the entity/class belongs to, in a multi-model design .
It's an optional attribute.
Level: Class Attribute
Description
Use the Model attribute to tell Aurelius the model where that entity (class) belongs to. This attribute allows you to build
applications, so that you can separate your mapping in multiple models. By using the Model attribute you can easily do it in a declarative way, specifying the model of each class.
You can add multiple Model attributes to the class, meaning that the class belongs to more than one model.
This attribute is optional and if omitted the class will be considered to belonging to the
.
Constructor constructor
Create(Name:
string
);
Parameters
Name
The name of the model
Usage
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[Entity, Automapping]
[Model( 'Sample' )]
TCustomer =
class
(TObject)
[Entity, Automapping]
[Model( 'Sample' )]
[Model( 'Security' )]
TUserInfo =
class
(TObject)
4.1.6
Association
Specifies a many-to-one association (relationship).
Level: Field/Property Attribute
Description
Use Association attribute to indicate that the field/property represents a many-to-one association with another class. For example, if you have property
Customer of type TCustomer, it means that your object is associated with one
(and only one) customer. Associations can only be defined for fields and properties of class types, and the associated class must also be an
class, so you can have a relationship between one class and another (between tables, at database level).
You must always use Association attribute together with
While the former is used to define generic, class-level meta-information about the association, the latter is used to define database-level relationships (fields that will be foreign keys)
Constructor constructor
Create;
overload
;
constructor
Create(AProperties: TAssociationProps);
overload
;
constructor
Create(AProperties: TAssociationProps; Cascade:
TCascadeTypes);
overload
;
Parameters
AProperties
Specifies some general properties for the association. Valid values are:
TAssociationProp = (Lazy, Required);
TAssociationProps =
set of
TAssociationProp;
Lazy The associated object is not loaded together with the current object.
is used. In a SELECT operation, Aurelius will only retrieve the Id of the associated object. The object will only be loaded when the application effectively needs it (e.g., when user references property MyObject.AssociatedObject). When it happens, Aurelius will perform another SELECT in the database just to retrieve the associated object data. Only at this point the object is instantiated and data is filled.
If Lazy is not specified, the default behavior is eagermode loading. It means that when the object is loaded,
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the associated object is also fully loaded. Aurelius will perform a INNER (or LEFT) JOIN to the related tables, fetch all needed fields, create an instance of the associated object and set all its properties. This is the default value.
Required Associated object is required. When Aurelius executes a
SELECT statement to load the object, it will use an INNER
JOIN to retrieve data for the associated object. When setting this flag it's recommended to set the column as required in the
If Required not specified, then is assumes by default that association is optional. It means that associated object is not required. When Aurelius executes a SELECT statement to load the object, it will use a LEFT JOIN to retrieve data for the associated object.
Cascade
Defines how Aurelius will behave on the association when the container object is saved, deleted or updated.
TCascadeType = (SaveUpdate, Merge, Remove,
RemoveOrphan, Refresh, Evict, Flush);
TCascadeTypes =
set of
TCascadeType;
CascadeTypeAll =
[Low(TCascadeType)..High(TCascadeType)] -
[TCascadeType.RemoveOrphan];
CascadeTypeAllRemoveOrphan = CascadeTypeAll +
[TCascadeType.RemoveOrphan];
CascadeTypeAllButRemove = CascadeTypeAll -
[TCascadeType.Remove];
It's recommended that you use one of the predefined cascades, like CascadeTypeAll, CascadeTypeAllButRemove or
CascadeTypeAllRemoveOrphan. For associations,
CascadeTypeAllButRemove is the most recommended one.
SaveUpdat When object is saved (inserted), or updated, the e associated object will be automatically saved/updated.
The associated object is actually saved before the container object, because the Id of associated object might be needed to save the container object.
Merge When object is merged, the associated object will also be merged.
Remove When object is removed from database, the associated object will also be removed.
Refresh When object is refreshed from database, the associated object will also be refreshed.
RemoveOr phan
Used only in
.
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Evict
Flush
When object is
evicted from manager, the associated
object will also be evicted.
If an object is
flushed explicitly, the associated object
will also be flushed. This cascade doesn't have any effect is Flush is called for all objects in manager
(without parameter).
Usage
[Association([], CascadeTypeAllButRemove)]
[JoinColumn( 'ID_SONG_FORMAT' , [])]
property
SongFormat: TSongFormat
read
FSongFormat
write
FSongFormat;
[Association([TAssociationProp.Lazy],
[TCascadeType.SaveUpdate])]
[JoinColumn( 'ID_ARTIST' , [])]
FArtist: Proxy<TArtist>;
Note
In the previous example, the Proxy<TArtist> type is used because association was declared as lazy (see
Associations and Lazy-Loading ). Alternatively you
can declare FArtist field just as TArtist, and in this case association will not be lazy-loaded.
4.1.7
JoinColumn
Specifies the table column used as foreign key for one association.
Level: Field/Property Attribute
Description
Use JoinColumn attribute to map a field/property to a table column in the database. The field/property must also have an
for it.
The table column defined by JoinColumn will be created as a foreign key to the referenced association. By default, the relationship created by Aurelius will reference the
Id of the associated object. But you can reference another value
in the object, as long as the value is an unique value.
The data type of the table column defined by JoinColumn will be the same as the data type of the referenced column in the associated table.
When the association is a class with
composite Id's , specify as many
JoinColumn attributes as the number of columns in the primary key of association class. For example, if the associated class has three table columns in the primary key, you must specify three JoinColumn attributes, one for each column.
Constructor constructor
Create(Name:
string
);
overload
;
constructor
Create(Name:
string
; Properties:
TColumnProperties);
overload
;
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Create(Name:
string
; Properties: TColumnProperties;
ReferencedColumnName:
string
);
overload
;
Parameters
Name
Properties
Contains the name of table column in the database used to hold the foreign key.
A set containing zero or more options for the column.
TColumnProps and TColumnProp are declared as follow:
TColumnProp = (Unique, Required, NoInsert,
NoUpdate);
TColumnProps =
set of
TColumnProp;
Unique Values of this column must be unique. Aurelius will create an unique key (index) in the database to ensure unique values for this column. In practice, if this flag is set the relationship will become a oneto-one relationship
Required Column must be NOT NULL. Values are required for this field/property. This flag must be set together with the orRequired flag in
NoInsert When inserting a record in the database, do not include this column in the INSERT command. The value of this field/property will not be saved in the database in INSERT commands.
NoUpdate When updating a record in the database, do not include this column in the UPDATE command. The value of this field/property will not be saved in the database in UPDATE commands.
Lazy Not used. This option is only used in
attribute.
ReferencedColum
Indicates the column name in the associated table that will
nName
be referenced as foreign key. The referenced column must be unique in the associated table. This parameter is optional, if it's not specified (and usually it won't), the name of
field will be used - in other words, the primary key of the associated table will be referenced by the foreign key.
Usage
[Association]
[JoinColumn( 'ID_SONG_FORMAT' , [])]
property
SongFormat: TSongFormat
read
FSongFormat
write
FSongFormat;
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[Association([TAssociationProp.Lazy], [])]
[JoinColumn( 'ID_ARTIST' , [])]
FArtist: Proxy<TArtist>;
Note
In the previous example, the Proxy<TArtist> type is used because association was declared as lazy (see
Associations and Lazy-Loading ). Alternatively you
can declare FArtist field just as TArtist, and in this case association will not be lazy-loaded.
4.1.8
ManyValuedAssociation
Specifies an one-to-many association (relationship), or in other words, a collection of objects.
Level: Field/Property Attribute
Description
Use ManyValuedAssociation attribute to indicate that the field/property represents a one-to-many association - a collection of objects of the same class. For example, if you have property Addresses of type TList<TCustomer>, it means that each object in collection is associated with the container object.
Many-valued associations can only be defined for fields and properties of type
TList<class>, and the associated class must also be an
can have a relationship between one class and another (between tables, at database level).
Defining a collection of child objects like this will require that the table holding child objects records will have a foreign key column referencing the container object. This can be done in two ways.
1. Use
ForeignJoinColumn attribute to define a foreign key in the child object
class.
2. Create an
Association in the child object class and then use MappedBy
parameter to indicate the field/property that holds the association. This will become a bidirectional association, since you have the child object referencing the parent object though an Association, and the parent object holding a collection of child objects through a ManyValuedAssociation.
Constructor constructor
Create;
overload
;
constructor
Create(AProperties: TAssociationProps);
overload
;
constructor
Create(AProperties: TAssociationProps; Cascade:
TCascadeTypes);
overload
;
constructor
Create(AProperties: TAssociationProps; Cascade:
TCascadeTypes; MappedBy:
string
);
overload
;
Parameters
FetchType
Specifies some general properties for the association. Valid values are:
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TAssociationProp = (Lazy, Required);
TAssociationProps =
set of
TAssociationProp;
Lazy The associated object is not loaded together with the current object.
is used. In a SELECT operation, Aurelius will only retrieve the Id of the associated object. The object will only be loaded when the application effectively needs it (e.g., when user references property MyObject.AssociatedObject). When it happens, Aurelius will perform another SELECT in the database just to retrieve the associated object data. Only at this point the object is instantiated and data is filled.
If Lazy is not specified, the default behavior is eagermode loading. It means that when the object is loaded, the associated object is also fully loaded. Aurelius will perform a INNER (or LEFT) JOIN to the related tables, fetch all needed fields, create an instance of the associated object and set all its properties. This is the default value.
Required This option is ignored in Many-valued Associations
Cascade
Defines how Aurelius will behave on the association list when the container object is saved, deleted or updated.
TCascadeType = (SaveUpdate, Merge, Remove,
RemoveOrphan, Refresh, Evict, Flush);
TCascadeTypes =
set of
TCascadeType;
CascadeTypeAll =
[Low(TCascadeType)..High(TCascadeType)] -
[TCascadeType.RemoveOrphan];
CascadeTypeAllRemoveOrphan = CascadeTypeAll +
[TCascadeType.RemoveOrphan];
CascadeTypeAllButRemove = CascadeTypeAll -
[TCascadeType.Remove];
It's recommended that you use one of the predefined cascades, like CascadeTypeAll, CascadeTypeAllButRemove or
CascadeTypeAllRemoveOrphan. For many-valuded associations,
CascadeTypeAll or CascadeTypeAllRemoveOrphan are the recommended ones.
SaveUpdat When object is save (inserted) or updated, the e associated object list will be automatically saved. First the parent object is saved, then all objects in the collection are also saved.
Merge When object is merged, all the associated objects in the object list are also merged.
Remove When object is removed from database, all objects in the list are also removed.
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Refresh When object is refreshed from database, the associated
RemoveOr phan object will also be refreshed.
When a detail (child) object is removed from a list, it will also be deleted (removed from database and destroyed). If RemoveOrphan is not present, then the
Evict child object will not be deleted, just the association with the parent object will be removed (i.e., the foreign key column will be set to null)
When object is
evicted from manager, the associated
Flush object will also be evicted.
If an object is
flushed explicitly, the associated object
will also be flushed. This cascade doesn't have any effect is Flush is called for all objects in manager
(without parameter).
MappedBy This parameter must be used when the association is bidirectional, i.e., the associated class referenced in the list has also an
Association to the object containing the list, see Description
above.
This parameter must contain the name of field or property, in the child object class, that holds an Association referencing the container object.
Usage
Example using MappedBy parameter:
TMediaFile =
class private
[Association([TAssociationProp.Lazy], [])]
[JoinColumn( 'ID_ALBUM' , [])]
FAlbum: Proxy<TAlbum>;
TAlbum =
class public
[ManyValuedAssociation([], CascadeTypeAll, 'FAlbum' )]
property
MediaFiles: TList<TMediaFile>
read
FMediaFiles
write
FMediaFiles;
Example using ForeignJoinColumn attribute (in this example, TTC_InvoiceItem class does not have an association to TTC_Invoice class, so "INVOICE_ID" field will be created in InvoiceItem table):
TTC_Invoice =
class private
[ManyValuedAssociation([], CascadeTypeAll)]
[ForeignJoinColumn( 'INVOICE_ID' , [TColumnProp.Required])]
FItems: TList<TTC_InvoiceItem>;
Note
In the previous example, the Proxy<TAlbum> type is used because association was declared as lazy (see
Associations and Lazy-Loading ). Alternatively you
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can declare FAlbum field just as TAlbum, and in this case association will not be lazy-loaded.
4.1.9
ForeignJoinColumn
Specifies the table column used as foreign key in the child object, for a manyvalued-association.
Level: Field/Property Attribute
Description
Use ForeignJoinColumn attribute to map a field/property to a table column in the database. The field/property must also have an
attribute defined for it.
The table column defined by ForeignJoinColumn will be created as a foreign key to the referenced association. Note that the column will be created in the
child table, and it will reference the parent table, i.e, the "container" of the object list.
By default, the relationship created by Aurelius will reference the
of the associated object. But you can reference another value in the object, as long as the value is an unique value.
The data type of the table column defined by ForeignJoinColumn will be the same as the data type of the referenced column in the associated table.
This attribute must only be used if the
ManyValuedAssociation is unidirectional.
If it's bidirectional, you should not use it, and just the MappedBy parameter when declaring the
attribute.
When the association is a class with
composite Id's , specify as many
ForeignJoinColumn attributes as the number of columns in the primary key of association class. For example, if the associated class has three table columns in the primary key, you must specify three ForeignJoinColumn attributes, one for each column.
Constructor constructor
Create(Name:
string
);
overload
;
constructor
Create(Name:
string
; Properties:
TColumnProperties);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProperties;
ReferencedColumnName:
string
);
overload
;
Parameters
Name
Properties
Contains the name of table column in the database used to hold the foreign key.
A set containing zero or more options for the column.
TColumnProps and TColumnProp are declared as follow:
TColumnProp = (Unique, Required, NoInsert,
NoUpdate);
TColumnProps =
set of
TColumnProp;
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Unique Values of this column must be unique. Aurelius will create an unique key (index) in the database to ensure unique values for this column.
Required Column must be NOT NULL. Values are required for this field/property.
NoInsert When inserting a record in the database, do not include this column in the INSERT command. The value of this field/property will not be saved in the database in INSERT commands.
NoUpdate When updating a record in the database, do not include this column in the UPDATE command. The value of this field/property will not be saved in the database in UPDATE commands.
Lazy Not used. This option is only used in
attribute.
ReferencedColum
Indicates the column name in the associated table that will
nName
be referenced as foreign key. The referenced column must be unique in the associated table. This parameter is optional, if it's not specified (and usually it won't), the name of
field will be used - in other words, the primary key of the associated table will be referenced by the foreign key.
Usage
TTC_Invoice =
class private
[ManyValuedAssociation([], CascadeTypeAll)]
[ForeignJoinColumn( 'INVOICE_ID' , [TColumnProp.Required])]
FItems: TList<TTC_InvoiceItem>;
4.1.10 OrderBy
Specifies the default order of the items in a
Level: Field/Property Attribute
Description
Use OrderBy attribute to define in which order the objects in a many-valued association (collection) will be loaded from the database. If no OrderBy attribute is present, no order will be defined (no ORDER BY clause will be added to the SELECT statement that retrieves the records) and items will be loaded according to the default ordering used by the database server. Note that after the items are loaded from the database, no further ordering is performed - this attribute only enforces ordering at database level, not memory level. Thus, if you later manually add new items to the collection in an unsorted order, they will remain that way.
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You can specify one or more member names (property or field names) in this attribute (not database column names). Multiple member names must be separated by comma (,). You can use the same member names that you can use when
in a query.
The default order direction is ascending. You can specify a descending order by appending " DESC" (with space) after the member name.
You can also order by members of associated objects. To do that, prefix the member name with the name of the association field/property followed by a
"." (dot). Nested associations can be used. For example, if your class has a property "Customer" which in turn has a property "Country", you can order by country's name using "Customer.Country.Name".
Constructor constructor
Create(MemberNames:
string
);
Parameters
MemberName s
Contains the name(s) of the member(s) used to order the collection.
Multiple member names must be separated by comma.
Associated members must be prefixed with association name followed by dot. You can optionally use "DESC" suffix to order by descending direction.
Usage
TTC_Invoice =
class private
[ManyValuedAssociation([], CascadeTypeAll)]
[OrderBy('Product.Name, Category DESC')]
FItems: TList<TTC_InvoiceItem>;
4.1.11 Inheritance
Identifies the class as the ancestor for a hierarchy of entity classes.
Level: Class Attribute
Description
Use Inheritance attribute to allow persistence of the current class and all its descendants (if they are marked with Entity attribute).
If you have a class hierarchy and want Aurelius to save all of those classes, you must add the Inheritance attribute to the top level (parent) class of all the hierarchy in order to use a specific
. If you are using
single table strategy , you also need to define a
DiscriminatorColumn attribute in the
base class, and a
DiscriminatorValue attribute in each descendant class. If you
are using
, you need to define a
attribute and a
attribute in each descendant class.
Constructor constructor
Create(Strategy: TInheritanceStrategy);
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Parameters
Strategy
Specifies the
inheritance strategy to be used in the class
hierarchy. Valid values are (prefixed by TInheritanceStrategy):
SingleTabl Use
single table strategy for the class hierarchy. You
e must also define a
DiscriminatorColumn attribute in the
class and a
DiscriminatorValue attribute in each
descendant class.
JoinedTabl Use
for the class hierarchy. In es this strategy for each descendant class you must define a
Usage
[Inheritance(TInheritanceStrategy.SingleTable)]
[DiscriminatorColumn( 'MEDIA_TYPE' , TDiscriminatorType.dtString)]
TMediaFile =
class
4.1.12 DiscriminatorColumn
Specifies the column table to be used as class discriminator in a
single table inheritance strategy .
Level: Class Attribute
Description
Use DiscriminatorColumn attribute to specify the column in the table used as class discriminator. When you use
Inheritance attribute and set strategy to
single table , you must also define this attribute. In single table strategy, all
classes are saved in the same table, and the value of discriminator column is the way Aurelius use to tell the class representing each record in the table. For example, if you have both classes TCar and TMotorcycle inheriting from
TVehicle and all classes being saved in the same table, when Aurelius reads a record it must tell if it represents a TCar or TMotorcycle. It does that using the value specified in the discriminator column. Each descending class must declare the attribute DiscriminatorValue that will define what is the value to be saved in the discriminator column that will represent the specified class.
Constructor constructor
Create(Name:
string
; DiscriminatorType:
TDiscriminatorType);
overload
;
constructor
Create(Name:
string
; DiscriminatorType:
TDiscriminatorType; Length: Integer);
overload
;
Parameters
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Name
Discriminator
Type
The name of the table column that will hold discriminator values which will identify the class. This column will be created by
Aurelius if you create the database
Specifies the column data type. Valid values are (prefixed by
TDiscriminatorType)
Length
dtString Discriminator column type will be string. Discriminator values must be strings.
dtInteger Discriminator column type will be integer. Discriminator values must be integer numbers.
Specifies the length of column data type, only used when
DiscriminatorType is string. If not specified, a default value is used.
Usage
[Inheritance(TInheritanceStrategy.SingleTable)]
[DiscriminatorColumn( 'MEDIA_TYPE' , TDiscriminatorType.dtString)]
TMediaFile =
class
4.1.13 DiscriminatorValue
Specifies the value that identifies a class in the discriminator column, when using
single table inheritance strategy
.
Level: Class Attribute
Description
Use DiscriminatorValue to define the value to be saved in the discriminator column when the class is saved. In a
single table inheritance strategy , all
classes are saved in the same table. Thus, when a subclass is saved, Aurelius updates an extra table column with a value that indicates that the record contains that specific class. This value is specified in this DiscriminatorValue attribute. It's also used by Aurelius when the record is being read, so it knows which class needs to be instantiated when loading objects from database.
Constructor constructor
Create(Value:
string
);
overload
;
constructor
Create(Value: Integer);
overload
;
Parameters
Value
The value to be used in the discriminator column. Value must be string or integer, depending on the type of the discriminator column declared in the DiscriminatorColumn attribute.
Usage
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// Ancestor class:
[Inheritance(TInheritanceStrategy.SingleTable)]
[DiscriminatorColumn( 'MEDIA_TYPE' , TDiscriminatorType.dtString)]
TMediaFile =
class
// Child classes:
[DiscriminatorValue( 'SONG' )]
TSong =
class
(TMediaFile)
[DiscriminatorValue( 'VIDEO' )]
TVideo =
class
(TMediaFile)
4.1.14 PrimaryJoinColumn
Defines the primary key of a child table that will be referencing the primary key of a parent table, in a
joined tables inheritance strategy .
Level: Class Attribute
Description
Use PrimaryJoinColumn attribute to specify the column that will be used as primary key of the child table. If you specified a
joined tables inheritance strategy using the
attribute in the base class, then each descendant class will be saved in a different table in the database, and it will be linked to the table containing the data of the parent class. This relationship is one-to-one, so the child table will have a primary key of the same data type of the parent table's primary key. The child table's primary key will also be a foreign key referencing the parent table. So PrimaryJoinColumn attribute is used to define the name of the primary key column. Data type doesn't need to be defined since it will be the same as the parent primary key.
You can omit the PrimaryJoinColumn attribute. In this case, the name of table column used will be the same as the name of table column in the base class/ table.
When the ancestor is a class with
composite Id's , you can specify one
PrimaryJoinColumn attribute for each table column in the ancestor class primary key. If you specify less PrimaryJoinColumn attributes than the number of columns in the primary key, the missing ones will be considered default, i.e, the name of the table column in the primary key will be used.
Constructor constructor
Create(Name:
string
);
Parameters
Name
The name of the child table column used as primary key and foreign key. If an empty string is provided, it will use the same name as the table column in the parent's class/table primary key
Usage
// Ancestor class:
[TABLE( 'MEDIA_FILES' )]
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[Inheritance(TInheritanceStrategy.JoinedTables)]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TMediaFile =
class private
[Column( 'MEDIA_ID' , [TColumnProp.Required])]
FId: integer;
// Child classes:
[TABLE( 'SONGS' )]
[PrimaryJoinColumn( 'MEDIAFILE_ID' )]
TSong =
class
(TMediaFile)
// In this case, a field with name MEDIA_ID will be created in table 'VIDEOS'
[TABLE( 'VIDEOS' )]
[PrimaryJoinColumn( '' )]
TVideo =
class
(TMediaFile)
// In this case, a field with name MEDIA_ID will be created in table 'LIST_SHOWS'
// Since PrimaryJoinColumn attribute is not present
[TABLE( 'LIVE_SHOWS' )]
TLiveShow =
class
(TMediaFile)
4.1.15 Sequence
Defines the sequence (generator) used to generate
Level: Class Attribute
Description
Use the Sequence attribute to define the database sequence (generator) to be created (if requested) and used by Aurelius to retrieve new
database does not support sequences, or the generator type specified in the
attribute does not use a database sequence, this attribute is ignored.
Constructor constructor
Create(SequenceName:
string
);
overload
;
constructor
Create(SequenceName:
string
; InitialValue,
Increment: Integer);
overload
;
Parameters
Sequence
Name
InitialValu e
The name of the sequence/generator in the database
The initial value of the sequence. Default value: 1
Increment
The increment used to increment the value each time a new value is retrieved from the sequence. Default value: 1.
Usage
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[Sequence( 'SEQ_MEDIA_FILES' )]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TMediaFile =
class
4.1.16 UniqueKey
Defines an exclusive (unique) index for the table.
Level: Class Attribute
Description
Use UniqueKey if you want to define a database-level exclusive (unique) index in the table associated with the class. Note that you do not need to use this attribute to define unique keys for field defined in the
columns defined as unique in the
attribute. Those are created automatically by Aurelius. If you want to create a non-exclusive (non-unique) index, use
attribute instead.
Constructor constructor
Create(Columns:
string
);
Parameters
Columns
The name of the table columns that compose the unique key. If two or more names are specified, they must be separated by comma.
Usage
[UniqueKey( 'INVOICE_TYPE, INVOICENO' )]
TTC_Invoice =
class
4.1.17 DBIndex
Defines a non-exclusive index for the table.
Level: Class Attribute
Description
Use DBIndex if you want to define a database-level non-exclusive index in the table associated with the class. The index will mostly be used to improve performance when executing queries. If you want to create an unique index, use
Constructor constructor
Create(
const
Name, Columns:
string
);
Parameters
Name
The name of the Index. When updating the database, this is what
Aurelius will check to decide if the index needs to be created or not.
Columns
The name of the table columns that compose the unique key. If two or more names are specified, they must be separated by comma.
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Usage
[DBIndex( 'IDX_INVOICE_DATE' , 'ISSUEDATE' )]
TTC_Invoice =
class
4.1.18 ForeignKey
Defines the name of a foreign key.
Level: Field/Property Attribute
Description
Use ForeignKey to define a custom name for the foreign key generated by an
or
. This attribute is optional even when
is not specified. When this attribute is not present, Aurelius will automatically choose a name for the foreign key.
Constructor constructor
Create(AName:
string
);
Parameters
AName
Specifies the name of the foreign key.
Usage
[Association([TAssociationProp.Lazy],
[TCascadeType.SaveUpdate])]
[ForeignKey( 'FK_SONG_ARTIST' )]
[JoinColumn( 'ID_ARTIST' , [])]
FArtist: Proxy<TArtist>;
4.1.19 Enumeration
Specifies how to save an enumerated type in the database.
Level: Enumerator Attribute
Description
Use Enumeration attribute if you have fields or properties of enumerated types and you want to save them in the database. Using Enumerator you define how the enumerated values will be saved and loaded from the database. The
Enumerator attribute must be declared right above the enumerated type.
Constructor constructor
Create(MappedType: TEnumMappingType);
overload
;
constructor
Create(MappedType: TEnumMappingType; MappedValues:
string
);
overload
;
Parameters
MappedTy pe
Indicated the type of the enumerated value in the database. Valid values are (prefixed by TEnumMappingType):
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emChar Enumerated values will be saved as single-chars in the database emInteger Enumerated values will be saved as integer values. The value used is the ordinal value of the enumerated type, i.e, the first value in the enumerator will be saved as 0, the second as 1, etc..
emString Enumerated values will be saved as strings in the database
MappedVa lues
If MappedType is char or string, then you must use this parameter to specify the char/string values corresponding to each enumerated value. The values must be comma-separated and must be in the same order as the values in the enumerated type.
Usage
[Enumeration(TEnumMappingType.emChar, 'M,F' )]
TSex = (tsMale, tsFemale);
4.1.20 Automapping
Indicates that the class is an entity class, and all its attributes are
Level: Class Attribute
Description
When Automapping attribute is present in the class, all mapping is done automatically by Aurelius, based on the class declaration itself. For more information about how automapping works, see
If AutoMappingMode in
is set to Full, then you don't need to define this attribute - every entity class is considered to be automapped.
Constructor constructor
Create;
Parametes
None.
Usage
[Entity]
[Automapping]
TCustomer =
class
(TObject)
4.1.21 Transient
Indicates a non-persistent field in an
Level: Field Attribute
Description
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When the class is being
Automapping attribute, by default
every field in the class is persisted. If you don't want an specific field to be persisted, declare a Transient attribute before it.
Constructor constructor
Create;
Parametes
None.
Usage
[Entity]
[Automapping]
TCustomer =
class
(TObject)
private
[Transient]
FTempCalculation: integer;
4.1.22 Version
Indicates that the class member (field/property) holds the version of the entity, to be used in
versioned concurrency control .
Level: Field/Property Attribute
Description
When adding this attribute to any member, Aurelius automatically enabled
versioned concurrency control on entities of that class. This means that
Aurelius will make sure that updates on that entity will only happen if no other user changed entity data in the meantime.
To accomplish that, the entity must hold the "version" value, so Aurelius knows which is the current version of that entity. You must thus add the Version attribute to any member of the class (field or property) so Aurelius knows where to save the version value.
The field/property type must be of Integer type.
Constructor constructor
Create;
Parametes
None.
Usage
[Entity]
[Automapping]
TCustomer =
class
(TObject)
private
[Version]
FVersion: integer;
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4.1.23 Description
Allows to associate a description to the class or field/property.
Level: Class, Field or Property attribute
Description
Use Description attribute to better document your classes, fields and properties, by adding a string description to it. Currently this information is not used by Aurelius but this Description attribute can be created when generating classes from database using TMS Data Modeler tool. You can later at runtime retrieve this information for any purposes.
Constructor constructor
Create(AText: string);
Parametes
AText
The text to be associated with class, field or property
Usage
[Entity]
[Automapping]
[Description( 'Customer data' )]
TCustomer =
class
(TObject)
private
4.2
Automapping
Automapping is an Aurelius feature that allows you to save a class without needing to specify all needed
attributes. Usually in an entity class you need to define table where data will be saved using
each field or property you want to save you need to specify the
attribute to define the table column in the database where the field/property will be mapped to, etc..
By defining a class as automapped, a lot of this mapping is done automatically based on class information, if it's not explicity specified. For example, the table name is automatically defined as the class name, with the "T" prefix removed.
To define a class as automapped, you just need to add the
attribute to the class.
Automapping is not an all-or-nothing feature. Aurelius only performs the automatic mapping if no attribute is specified. For example, you can define a class as automapped, but you can still declare the
different table name, or you can use
Column attribute in some specific fields or
properties to override the default automatic mapping.
Below we list some of rules that automapping use to perform the mapping.
Table mapping
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The name of table is assumed to be the name of the class. If the first character of the class name is an upper case "T", it is removed. For example, class "TCustomer" will be mapped to table "Customer", and class "MyInvoice" will be mapped to table "MyInvoice"
Column mapping
Every field in the class is mapped to a table column. Properties are ignored and not saved. If you don't want a specific class field to be saved automatically, add a
Transient attribute to that class field.
The name of the table column is assumed to be name of the field. If the first character of the field name is an upper case "F", it is removed. For example, field "FBirthday" is mapped to table column "Birthday".
If the class field type is a
Nullable<T> type, then the table column will be
optional (nullable). Otherwise, the table column will be required (NOT NULL).
For currency fields, scale and precision are mapped to 4 and 18. For float fields, scale and precision are mapped to 8 and 18, respectively. If field is a string, length used will be the default length specified in the
If the field is an object instance instead of an scalar value/primitive type, then it will be mapped as an association, see below.
Associations
If the class field in an object instance (except a list), it will be mapped as an
to that class. The column name for the foreign key will be the field name (without "F") followed by "_ID". For example, if the class has a field
FCustomer: TCustomer
Aurelius will create an association with TCustomer and the name of table column holding the foreign key will be "Customer_ID".
If the class field is a list type (TList<T>) it will be mapped as a
. A foreign key will be created in the class used for the list. The name of table column holding the foreign key is field name + table name +
"_ID". For example, if class TInvoice has a field:
FItems: TList<TInvoiceItem>
Aurelius will create a many-valued association with TInvoiceItem, and a table column holding the foreign key will be created in table "InvoiceItem", with the name "Items_Invoice_ID".
If the field type is a Proxy<T> type, fetch type of the association will be defined as
lazy , otherwise, it will be eager.
Identifier
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4.3
If no
Id attribute is specified in the class, Aurelius will use a field named "FID" in
the class as the class identifier. If such class field does not exist and no
attribute is defined, an error will be raised when the class is saved.
Enumerations
Enumerations are not automapped unless the auto mapping mode is configured to Full in
global configuration . In this case, if an enumeration type does not
have an Enumeration attribute defined, it will be automapped as string type, and the mapped value will be the name of the enumerated value. For example, the enumerated type:
TSex = (seFemale, seMale); will be mapped as string with mapped values 'seFemale', 'seMale'.
Sequences
If not specified, the name of the sequence to be created/used (if needed) will be "SEQ_" + table name. Initial value and increment will defined as 1.
Inheritance
Inheritance is not automapped and if you want to use it you will need explicitly define
Inheritance attribute and the additional attributes needed for complete
inheritance mapping.
Nullable<T> Type
Table columns in databases can be marked as optional (nullable) or required
(not null). When you map a class property to a table column in the database, you can choose if the column will be required or not.
If the column is optional, the column value hold one valid value, or it can be null. Problem is that primitive types in Delphi cannot be nullable. Using
Nullable<T> type which is declared in unit Aurelius.Types.Nullable, you can create a property in your class that can represent the exact value in the database, i.e., it can hold a value, or can be nullable.
For example, suppose you have the following class field mapped to the database:
[Column( 'BIRTHDAY' , [])]
FBirthday: TDate;
The column BIRTHDAY in the database can be null. But the field FBirthday in the class cannot be null. You can set FBirthday to zero (null date), but this is different from the NULL value in the database.
Thus, you can use the Nullable<T> type to allow FBirthday field to receive null values:
[Column( 'BIRTHDAY' , [])]
FBirthday: Nullable<TDate>;
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You can use FBirthday directly in expressions and functions that need TDate,
Delphi compiler will do the implicit conversion for you:
FBirthday := EncodeDate( 2000 , 1 , 1 );
If the compiler fails in any situation, you can read or write the TDate value using Value property:
FBirthday.Value := Encode( 2000 , 1 , 1 );
To check if the field has a null value, use HasValue or IsNull property:
IsBirthdayNull :=
not
FBirthday.HasValue;
IsBirthdayNull := FBirthday.IsNull;
There is global Nullable variable names SNull which represents the null value, you can also use it to read or write null values:
if
FBirthday <> SNull
then
// birthday is not null
FBirthday := SNull;
// Set to null
4.4
Binary Large Objects (Blobs)
You can map binary (or text) large objects (Blobs) table columns to properties in your class. As with other properties, Aurelius will properly save and load the content of the property to the specified table column in the database. In order for it to know that the class member maps to a blob, you must declare the data type as an array of byte:
[Column( 'Document' , [])]
FDocument: TArray<byte>; or as the TBlob type (recommended):
[Column( 'Photo' , [])]
FPhoto: TBlob;
In both examples above, Aurelius will check the field data type and create a blob field in the table to hold the content of the binary data. Each
uses a different data type for holding the blobs. Aurelius will choose the most generic one, i.e, that can hold any data (binary) and the largest possible amount of data. If the blob field already exists in the database, Aurelius will just load the field content in binary format and set it in the property.
In theory, you could use the TBytes type as well (and any other type that is an array of byte), however Delphi doesn't provide RTTI type info for the TBytes specifically. It might be a bug or by design, but you just can't use it. Use
TArray<byte> or any other dynamic byte array instead (or TBlob of course).
Using TBlob type you have more flexibility and features, as described in topics below.
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4.4.1
Lazy-Loading Blobs
When declaring blob attributes in your class, you can configure them for lazyloading. It means that whenever Aurelius tries to retrieve an object from the database, it will not include the blob field in the select, and thus the blob content will not be sent through network from server to client unless it's needed. If you access the blob content through the blob property, then
Aurelius will execute an SQL statement on-the-fly only to retrieve the blob content.
To map the blob property/field as lazy, you just need two requirements:
1. Use the TBlob type as the field/property type.
2. Add TColumnProp.Lazy to the column properties in the
The code below indicates how to declare a lazy-loaded blob:
TTC_Customer =
class
strict
private
// <snip>
[Column( 'Photo' , [TColumnProp.Lazy])]
FPhoto: TBlob;
The
type is implicitly converted to an array of byte but also have methods for retrieving the blob content as TBytes, string, etc.. Whenever you try to access the blob data through the TBlob type, the blob content will be retrieved from the database.
4.4.2
TBlob Type
The TBlob type is used to declare
blob field/properties. It's not required that
you use a TBlob type, but doing so will allow you to configure
and also provides you with helper methods for handling the binary content.
Usage
TCustomer =
class private
[Column( 'Photo' , [TColumnProp.Lazy])]
FPhoto: TBlob;
public property
Photo: TBlob
read
FPhoto
write
FPhoto;
Implicit conversion to TBytes
A TBlob implicitly converts to TBytes so you can directly use it in any method that uses it:
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BytesStream := TBytesStream.Create(Customer1.Photo);
// Use BytesStream anywhere that needs a TStream
Explicitly using AsBytes property
Alternatively you can use AsBytes property to get or set the value of the blob:
Customer1.Photo.AsBytes := MyBytesContent;
// MyBytesContent is a TBytes variable
Use AsString property to read/set the blob content as string
If you want to work with the blob content as string, you can just use AsString property for that:
Customer1.Photo.AsString := 'Set string directly to the blob' ;
Raw access to the data using Data and Size properties
If you want to have directly access to data, for high performance operations, without having to copy a byte array or converting data to a string, you can use read-only properties Data and Size. Data is a pointer (PByte) to the first byte of the data, and Size contains the size of blob data.
The code below saves the blob content into a stream:
MyStream := TFileStream.Create( 'BlobContent.dat' , fmCreate);
try
MyStream.Write(Customer1.Photo.Data^, Customer1.Photo.Size);
finally
MyStream.Free;
end
;
Using streams to save/load the blob
You can also use TBlob.LoadFromStream and SaveToStream methods to directly load blob content from a stream, or save to a stream:
MyStream := TFileStream.Create( 'BlobContent.dat' , fmCreate);
try
Customer1.Photo.LoadFromStream(MyStream);
Customer1.Photo.SaveToStream(AnotherStream);
finally
MyStream.Free;
end
;
IsNull property
Use IsNull property to check if a blob is empty (no bytes):
if not
Customer1.Photo.IsNull
then
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// Do something
Clearing the blob
You can clear the blob content (set blob content to zero bytes) by setting
IsNull property to true, or by calling Clear method:
// Clear Photo and Description blobs content.
// Both statement are equivalent
Customer1.Photo.IsNull := true;
Customer1.Photo.Clear;
Loaded and Available properties
TBlob provides two boolean properties: Loaded and Available, and they refer to the status of data availability when blob content is configured to be
Available property allows you to check if blob content is available, without forcing the content to be loaded. If Available is true, it means that the blob content is already available in memory, even if it's empty. If it's false, it means the blob content is not available in memory and a request must be performed to load the content.
Loaded property behaves in a similar way. When Loaded is true, it means that the blob content of a lazy-loaded blob was already loaded from the database.
If Loaded is false, it means the content was not loaded.
The difference between Loaded and Available is that when a new TBlob record is created, Available is true (because data is available - it's empty) and Loaded is false (because no content was loaded - because there is no content to load).
4.5
Associations and Lazy-Loading
Aurelius supports associations between objects, which are mapped to foreign keys in the database. Suppose you have the following TInvoice class:
TInvoice =
class private
FCustomer: TCustomer;
FInvoiceItems: TList<TInvoiceItem>; the class TInvoice has an association to the class TCustomer. By using
Association mapping attribute, you can define this association and Aurelius
deals with it automatically - customer data will be saved in its own table, and in Invoice table only thing saved will be a value in a foreign key field, referencing the primary key in Customer table.
Also, TInvoice has a list of invoice items, which is also a type of association.
You can define such lists using
ManyValuedAssociation mapping attribute. In
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this case, the TInvoiceItem objects in the list will have a foreign key referencing the primary key in InvoiceTable.
Eager Loading
When an object is retrieved from the database, its properties are retrieved and set. This is also true for associations. By default, eager-loading is performed, which means associated objects and lists are loaded and filled when object is loaded. In the TInvoice example above, when a TInvoice instance is loaded,
Aurelius also creates a TCustomer instance, fill its data and set it to the
FCustomer field. Aurelius uses a single SQL statement to retrieve data for all associations. FInvoiceItems list is also loaded. In this case, an extra SELECT statement is performed to load the list.
Lazy Loading
You can optionally define associations to be lazy-loaded. This means that
Aurelius will not retrieve association data from database until it's really needed
(when the property is accessed). You define lazy-loading associations this way:
1. Declare the class field as a Proxy<TMyClass> type, instead of TMyClass
(Proxy<T> type is declared in unit Aurelius.Types.Proxy)
2. Declare the
) attribute above the field, and define fetch mode as lazy in attribute parameters
3. Declare a property of type TMyClass with getter and setter that read/write from/to the proxy value field.
Example:
TMediaFile =
class private
[Association([TAssociationProp.Lazy], [])]
[JoinColumn( 'ID_ALBUM' , [])]
FAlbum: Proxy<TAlbum>;
function
GetAlbum: TAlbum;
procedure
SetAlbum(
const
Value: TAlbum);
public property
Album: TAlbum
read
GetAlbum
write
SetAlbum;
implementation function
TMediaFile.GetAlbum: TAlbum;
begin
Result := FAlbum.Value;
end
;
procedure
TMediaFile.SetAlbum(
const
Value: TAlbum);
begin
FAlbum.Value := Value;
end
;
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In the example above, Album will not be loaded when TMediaFile object is loaded. But if in Delphi code you do this:
TheAlbum := MyMediaFileObject.Album; then Aurelius will perform an extra SELECT statement on the fly, instantiate a new TAlbum object and fill its data.
Lazy loading lists
Lists can be set as lazy as well, which means the list will only be filled when the list object is accessed. It works in a very similar way to lazy-loading in normal associations. The only difference is that since you might need an instance to the TList object to manipulate the collection, you must initialize it and then destroy it. Note that you should not access Value property directly when creating/destroying the list object. Use methods SetInitialValue and
DestroyValue. The code below illustrates how to do that.
TInvoice =
class private
[ManyValuedAssociation([TAssociationProp.Lazy],
CascadeTypeAll)]
[ForeignJoinColumn( 'INVOICE_ID' , [TColumnProp.Required])]
FItems: Proxy<TList<TInvoiceItem>>;
private function
GetItems: TList<TInvoiceItem>;
public constructor
Create;
virtual
;
destructor
Destroy;
override
;
property
Items: TList<TInvoiceItem>
read
GetItems;
end
;
implementation constructor
TInvoice_Lazy.Create;
begin
FItems.SetInitialValue(TList<TInvoiceItem>.Create);
end
;
destructor
TInvoice_Lazy.Destroy;
begin
FItems.DestroyValue;
inherited
;
end
;
function
TInvoice_Lazy.GetItems: TList<TInvoiceItem>;
begin
result := FItems.Value;
end
;
Proxy<T> Available property
Available property allows you to check if proxied object is available, without forcing it be loaded. If Available is true, it means that the proxy object is
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already available in memory, even if it's empty. If it's false, it means the object is not available in memory and a request must be performed to load the content. In other words, Available property indicates if accessing the object will fire a new server request to retrieve the object.
4.6
Inheritange Strategies
There are currently two strategies for you to map class inheritance into the relational database:
Single Table : All classes in the hierarchy are mapped to a single table in the
database
Joined Tables : Each class is mapped to one different table, each one linked to
the parent's table.
Inheritance is defined in Aurelius using the
4.6.1
Single Table Strategy
With this strategy, all classes in the class hierarchy are mapped to a single table in relational database
The concrete class of the object is indicated by the values in a special column in the table named discriminator column. This column is specified by the programmer and its content is used to identify the real class of the object. The discriminator column must be of string or integer type.
The advantage of this strategy is that the database is simple, and performance is optimized, since queries don't need to have too many joins or unions.
One disadvantage is that all columns belonging to child classes must be declared as not required, since they must be null if the row in the table corresponds to a super class.
4.6.2
Joined Tables Strategy
In this strategy there is one table for each class in the class hierarchy.
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4.7
Each table represents a class in the hierarchy, and columns in the table are associated to the properties declared in the class itself. Even abstract classes have their own table, since they might have declared properties as well.
Tables are joined together using foreign keys. Each table representing a child class has a foreign key referencing the table representing the parent class. The foreign key is also the primary key, so the relationship cardinality between the tables is 1:1. In the previous illustration, the table Cricketer has a foreign key referencing the primary key in table Player.
The advantage of this strategy is that the database is normalized and the database model is very similar to the class model. Also, unlike the
, all columns in tables are relevant to all table rows.
One disadvantage is performance. To retrieve a single object several inner or left joins might be required, becoming even worse when complex queries are used. Database refactoring is also more difficult - if you need to move a property to a different class in hierarchy, for example, more than one table needs to be updated.
Composite Id
You can use composite identifier in TMS Aurelius. Although possible, it's strongly recommended that you use single-attribute, single-column identifiers.
The use of composite id should be used only for legacy applications where you already have a database schema that uses keys with multiple columns. Still in those cases you could try to add an auto-generated field in the table and use it as id.
Using composite Id's is straightforward: you just use the same attributes used for single Id:
and
attributes. The only difference is that you add those attributes two or more times to the classes. For example, the following TAppointment class has a composite Id using the attributes AppointmentDate and Patient (you can use associations as well):
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[Entity]
[Table( 'PERSON' )]
[Id( 'FLastName' , TIdGenerator.None)]
[Id( 'FFistName' , TIdGenerator.None)]
TPerson =
class
strict
private
[Column( 'LAST_NAME' , [TColumnProp.Required], 50)]
FLastName: string;
[Column( 'FIRST_NAME' , [TColumnProp.Required], 50 )]
FFirstName:
string
;
public property
LastName: string
read
FLastName
write
FLastName;
property
FirstName:
string read
FFiratName
write
FFiratName;
end
;
[Entity]
[Table( 'APPOINTMENT' )]
[Id( 'FAppointmentDate' , TIdGenerator.None)]
[Id( 'FPatient' , TIdGenerator.None)]
TAppointment =
class
strict
private
[Association([TAssociationProp.Lazy,
TAssociationProp.Required], [TCascadeType.Merge,
TCascadeType.SaveUpdate])]
[JoinColumn( 'PATIENT_LASTNAME' , [TColumnProp.Required])]
[JoinColumn( 'PATIENT_FIRSTNAME' , [TColumnProp.Required])]
FPatient: Proxy<TPerson>;
[Column( 'APPOINTMENT_DATE' , [TColumnProp.Required])]
FAppointmentDate: TDateTime;
function
GetPatient: TPerson;
procedure
SetPatient(
const
Value: TPerson);
public property
Patient: TPerson
read
GetPatient
write
SetPatient;
property
AppointmentDate: TDateTime
read
FAppointmentDate
write
FAppointmentDate;
end
;
Note that while TAppointment has a composite Id of two attributes, the number of underlying database table columns is three. This is because Patient attribute is part of Id, and the TPerson class itself has a composite Id. So primary key columns of table APPOINTMENT will be APPOINTMENT_DATE,
PATIENT_LASTNAME and PATIENT_FIRSTNAME.
Also pay attention to the usage of
JoinColumn attributes in field FPatient. Since
TPerson has a composite Id, you must specify as many JoinColumn attributes as the number of table columns used for the referenced table. This is the same for
As illustrated in the previous example, you can have association attributes as part of a composite identifier. However, there is one limitation: you can't have
lazy-loaded associations as part of the Id. All associations that are part of an
Id are loaded in eager mode. In the previous example, although FPatient association was declared with TAssociationProp.Lazy, using a proxy, this
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settings will be ignored and the TPerson object will be fully loaded when a
TAppointment object is loaded from the database.
When using composite Id, the generator specified in the
and all are considered as TIdGenerator.None.
When using Id values for finding objects, for example when using Find method of
object manager or using IdEq expression in a query, you are required to
provide an Id value. The type of this value is Variant. For composite Id's, you must provide an array of variant (use VarArrayCreate method for that) where each item of the array refers to the value of a table column. For associations in
Id's, you must provide a value for each id of association (in the example above, to find a class TAppointment you should provide a variant array of length = 3, with the values of appointment data, patient's last name and first name values.
4.8
Mapping Examples
This topic lists some code snippets that illustrates how to use attributes to build the object-relational mapping.
Examples:
Single-Table Inheritance and Associations
4.8.1
Basic Mapping
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TMS Aurelius Documentation unit
Artist;
interface uses
Aurelius.Mapping.Attributes,
Aurelius.Types.Nullable;
type
[Entity]
[Table( 'ARTISTS' )]
[Sequence( 'SEQ_ARTISTS' )]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TArtist =
class private
[Column( 'ID' , [TColumnProp.Unique, TColumnProp.Required,
TColumnProp.NoUpdate])]
FId: Integer;
FArtistName:
string
;
FGenre: Nullable<
string
>;
public property
Id: integer
read
FId;
[Column( 'ARTIST_NAME' , [TColumnProp.Required], 100 )]
property
ArtistName:
string read
FArtistName
write
FArtistName;
[Column( 'GENRE' , [], 100 )]
property
Genre: Nullable<
string
>
read
FGenre
write
FGenre;
end
;
implementation end
.
4.8.2
Single-Table Inheritance and Associations
In the example below, TSong and TVideo inherit from TMediaFile. The
TMediaFile class has two associations: Album and Artist. Both are lazy associations
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MediaFile;
interface uses
Generics.Collections,
Artist, Album,
Aurelius.Mapping.Attributes,
Aurelius.Types.Nullable,
Aurelius.Types.Proxy;
type
[Entity]
[Table( 'MEDIA_FILES' )]
[Sequence( 'SEQ_MEDIA_FILES' )]
[Inheritance(TInheritanceStrategy.SingleTable)]
[DiscriminatorColumn( 'MEDIA_TYPE' ,
TDiscriminatorType.dtString)]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TMediaFile =
class private
[Column( 'ID' , [TColumnProp.Unique, TColumnProp.Required,
TColumnProp.DontUpdate])]
FId: Integer;
FMediaName:
string
;
FFileLocation:
string
;
FDuration: Nullable<integer>;
[Association([TAssociationProp.Lazy], [])]
[JoinColumn( 'ID_ALBUM' , [])]
FAlbum: Proxy<TAlbum>;
[Association([TAssociationProp.Lazy], [])]
[JoinColumn( 'ID_ARTIST' , [])]
FArtist: Proxy<TArtist>;
function
GetAlbum: TAlbum;
function
GetArtist: TArtist;
procedure
SetAlbum(
const
Value: TAlbum);
procedure
SetArtist(
const
Value: TArtist);
public property
Id: integer
read
FId;
[Column( 'MEDIA_NAME' , [TColumnProp.Required], 100 )]
property
MediaName:
string read
FMediaName
write
FMediaName;
[Column( 'FILE_LOCATION' , [], 300 )]
property
FileLocation:
string read
FFileLocation
write
FFileLocation;
[Column( 'DURATION' , [])]
property
Duration: Nullable<integer>
read
FDuration
write
FDuration;
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Album: TAlbum
read
GetAlbum
write
SetAlbum;
property
Artist: TArtist
read
GetArtist
write
SetArtist;
end
;
[Entity]
[DiscriminatorValue( 'SONG' )]
TSong =
class
(TMediaFile)
private
FSongFormat: TSongFormat;
public
[Association]
[JoinColumn( 'ID_SONG_FORMAT' , [])]
property
SongFormat: TSongFormat
read
FSongFormat
write
FSongFormat;
end
;
[Entity]
[DiscriminatorValue( 'VIDEO' )]
TVideo =
class
(TMediaFile)
private
FVideoFormat: TVideoFormat;
public
[Association]
[JoinColumn( 'ID_VIDEO_FORMAT' , [])]
property
VideoFormat: TVideoFormat
read
FVideoFormat
write
FVideoFormat;
end
;
implementation
{ TMediaFile }
function
TMediaFile.GetAlbum: TAlbum;
begin
Result := FAlbum.Value;
end
;
function
TMediaFile.GetArtist: TArtist;
begin
Result := FArtist.Value;
end
;
procedure
TMediaFile.SetAlbum(
const
Value: TAlbum);
begin
FAlbum.Value := Value;
end
;
procedure
TMediaFile.SetArtist(
const
Value: TArtist);
begin
FArtist.Value := Value;
end
;
end
.
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4.8.3
Joined-Tables Inheritance
In this example, TBird and TMammal classes inherit from TAnimal. Each class has its own table. Specific bird data is saved in "BIRD" table, and common animal data is saved in "ANIMAL" table.
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TMS Aurelius Documentation unit
Animals;
interface uses
Generics.Collections,
Aurelius.Mapping.Attributes,
Aurelius.Types.Nullable,
Aurelius.Types.Proxy;
type
[Entity]
[Table( 'ANIMAL' )]
[Sequence( 'SEQ_ANIMAL' )]
[Inheritance(TInheritanceStrategy.JoinedTables)]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TAnimal =
class
strict
private
[Column( 'ID' , [TColumnProp.Unique, TColumnProp.Required,
TColumnProp.DontUpdate])]
FId: Integer;
[Column( 'ANIMAL_NAME' , [TColumnProp.Required], 50 )]
FName:
string
;
public property
Id: Integer
read
FId
write
FId;
property
Name:
string read
FName
write
FName;
end
;
[Entity]
[Table( 'BIRD' )]
[PrimaryJoinColumn( 'ANIMAL_ID' )]
TBird =
class
(TAnimal)
strict
private
[Column( 'CAN_FLY' , [], 0 )]
FCanFly: Nullable<boolean>;
[Column( 'BIRD_BREED' , [], 50 )]
FBirdBreed: Nullable<
string
>;
public property
CanFly: Nullable<boolean>
read
FCanFly
write
FCanFly;
property
BirdBreed: Nullable<
string
>
read
FBirdBreed
write
FBirdBreed;
end
;
[Entity]
[Table( 'MAMMAL' )]
[PrimaryJoinColumn( 'ANIMAL_ID' )]
TMammal =
class
(TAnimal)
strict
private
[Column( 'LAST_PREGNANCY_DAYS' , [], 0 )]
FLastPregnancyDays: Nullable<integer>;
public property
LastPregnancyDays: Nullable<integer>
read
FLastPregnancyDays
write
FLastPregnancyDays;
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;
implementation end
.
4.9
Registering Entity Classes
Aurelius doesn't require you to register the entity classes. Just by adding
attribute to the class it knows that the class is mapped and it will add it automatically to the
default model or a model you have explicitly specified
.
However, if you don't use the class anywhere in your application, the linker optimizer will remove it from the final application executable, and Aurelius will never know about it (since it retrieves information at runtime). There are situations where this can happen very often:
·
You have just started your application and wants Aurelius to create the database structure for you, but you still didn't use any of your classes.
Aurelius will not create the tables since the classes just don't exist in executable.
·
You are creating a server application, especially using XData, without any specific server-side logic. You will notice that XData will respond to 404 (not found) to the URL resource addresses corresponding to your classes. This is just because XData server doesn't know about those classes.
To solve these kind of problems, all you would have to do is use the class somewhere in your application. It could be a simple "TMyClass.Create.Free".
Nevertheless, to help you out in this task, there is a function RegisterEntity in unit Aurelius.Mapping.Attributes that you can use to make sure your class will be "touched" and thus included in final executable.
So in the same unit you have your classes mapped you can optinally just call
RegisterEntity in initialization section for all classes to make sure they will be present in application:
unit
MyEntities;
uses
{...}
, Aurelius.Mapping.Attributes;
type
[Entity, Automapping]
TCustomer =
class private
FId: integer;
{...}
initialization
RegisterEntity(TCustomer);
RegisterEntity(TCountry);
RegisterEntity(TInvoice);
{...}
end
.
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Chapter
V
Multi-Model Design
TMS Aurelius Documentation
5
5.1
Multi-Model Design
Most Aurelius applications uses single-model mapping. This means that all classes you
belongs to the same model. So for example when
retrieving objects from the database, or creating the
database structure , objects all
mapped classes will be available.
But in some situations, you might need to have multiple mapping models. For example, you want your TCustomer entity class to belong to your default model, but you want TUserInfo entity class to belong to a different model
("Security" model for example). There are several reasons for this, for example:
·
You have more than one database you want to access from your application, with totally different structures
·
You have some objects that you don't want to save to a database, but just want to use them in memory (using SQLite memory database)
·
You use other tools that uses Aurelius and you want to logically separate your entity classes for that. For example, when using TMS XData, you might want to use different models to create different server setups.
·
Any other reason you have to separate your classes into different mappings.
There are two ways to define multiple mapping models:
(preferrable), or manually creating a
. The following topics describe the two options and explain the concepts of multi-model design in
Aurelius.
Multi-Model Step-By-Step
This topic explains very shortly how to use multiple mapping models with
Aurelius. For more details about each step, please refer to main
1. Add a Model attribute to each class indicating the model where the class belongs to:
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[Entity, Automapping]
[Model( 'Sample' )]
TSampleCustomer =
class
{...}
[Entity, Automapping]
[Model( 'Security' )]
TUserInfo =
class
{...}
// no model attribute means default model
[Entity, Automapping]
TCustomer =
class
{...}
2. Retrieve the
TMappingExplorer object associated with the model:
uses
{...}
, Aurelius.Mapping.Explorer;
var
SampleExplorer: TMappingExplorer;
SecurityExplorer: TMappingExplorer;
DefaultExplorer: TMappingExplorer;
begin
SampleExplorer := TMappingExplorer.Get( 'Sample' );
SecurityExplorer := TMappingExplorer.Get( 'Security' );
DefaultExplorer := TMappingExplorer.
Default
;
3. Create an
object manager using the proper mapping explorer:
SampleManager := TObjectManager.Create(SampleConnection,
SampleExplorer);
SecurityManager := TObjectManager.Create(SecurityConnection,
SecurityExplorer);
DefaultManager := TObjectManager.Create(MyConnection,
DefaultExplorer); or simply:
SampleManager := TObjectManager.Create(SampleConnection,
TMappingExplorer.Get( 'Sample' ));
SecurityManager := TObjectManager.Create(SecurityConnection,
TMappingExplorer.Get( 'Security' ));
DefaultManager := TObjectManager.Create(MyConnection,
TMappingExplorer.
Default
); for default manager you can simply omit the explorer:
DefaultManager := TObjectManager.Create(MyConnection);
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4. You can also use the explorers in other needed places. For example, to create a
// this example creates tables for "Sample" model in
// a SQL Server database using FireDac,
// and "Security" model in a in-memory SQLite database
SampleConnection :=
TFireDacConnectionAdapter.Create(FDConnection1, false);
DBManager := TDatabaseManager.Create(SampleConnection,
TMappingExplorer.Get( 'Sample' ));
DBManager.UpdateDatabase;
DBManager.Free;
SecurityConnection :=
TSQLiteNativeConnectionAdapter.Create( ':memory:' );
DBManager := TDatabaseManager.Create(SecurityConnection,
TMappingExplorer.Get( 'Security' ));
DBManager.UpdateDatabase;
DBManager.Free;
5.2
Using Model attribute
Defining multiple mapping models in Aurelius is very straightforward if you use
Model attribute. Basically all you need to do is annotate a class with the model
attribute telling Aurelius the model where that class belongs to. For example, the following code specifies that class TUserInfo belongs to model "Security":
// TUserInfo belongs to model "Security"
[Entity, Automapping]
[Model( 'Security' )]
TUserInfo =
class
{...}
You can also include the class in multiple models, just by adding the Model attribute multiple times. The following example specifies that the class TSample belongs to both models "Security" and "Sample":
// TSample belongs to model "Security" and "Sample"
[Entity, Automapping]
[Model( 'Security' )]
[Model( 'Sample' )]
TSample =
class
{...}
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In Aurelius, every mapped class belongs to a model. If you omit the Model attribute (since it's optional), the class will be included in the default model.
// This class belongs to default model
[Entity, Automapping]
TCustomer =
class
{...}
If you want to add a class to both default model and a different model, you can just add it to default model (named "Default"):
// TUser belongs to both "Security" and default model
[Entity, Automapping]
[Model( 'Security' )]
[Model( 'Default' )]
TUser =
class
{...}
You can then use the different models by retrieving the
instance associated with a model.
5.3
TMappingExplorer
After Aurelius retrieves information about your
mapping , it saves all that info in
an object of class TMappingExplorer (declared in unit
Aurelius.Mapping.Explorer). In other words, a TMappingExplorer object holds all mapping information. Although in some cases you might never need to deal with it directly, it is a key class when using Aurelius because that's the class it uses to perform all its operations on the entities.
When you create an
object manager , for example, you do it this way:
Manager := TObjectManager.Create(DBConnection,
MyMappingExplorer);
And that is the same for the
database manager . You can omit the parameter
and create it like this:
Manager := TObjectManager.Create(DBConnection);
But this just means that you are telling the manager to use the default mapping explorer. It's the equivalent of doing this:
Manager := TObjectManager.Create(DBConnection,
TMappingExplorer.
Default
);
Retrieving a TMappingExplorer instance
As explained above, in single-model applications you will rarely need to deal with TMappingExplorer instances. All the mapping is available in the default
TMappingExplorer instance, which is used automatically by the object manager and database manager. But when you have multiple mapping models in your application, you will need to tell the manager what mapping model it will be
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using. To help you in that task, Aurelius provides you with global
TMappingExplorer instances. Aurelius creates (in a lazy way) on instance for each mapping model you have.
To retrieve the TMappingExplorer instance associated with a model, just use the TMappingExplorer.Get class property passing the model name. In the following example, the object manager will use the "Security" model, instead of the default one.
Manager := TObjectManager.Create(DBConnection,
TMappingExplorer.Get( 'Security' ));
Note that you don't need to destroy the TMappingExplorer instance in this case, those are global instances that are destroyed automatically by Aurelius when application terminates. To retrieve the default instance, use the Default property:
Manager := TObjectManager.Create(DBConnection,
TMappingExplorer.Default);
Creating a TMappingExplorer explicitly
Usually you don't need to create a mapping explorer explicitly. As mentioned above, Aurelius automatically creates a default mapping explorer (available in class property TMappingExplorer.Default) and always uses it in any place where a TMappingExplorer object is needed but explicitly provided (like when creating the object manager). And you can also retrieve a mapping explorer instance for a specific model. So it's very rare you need to create one your own.
But if you still need to do so, you can explicitly create a TMappingExplorer object using either a
mapping setup or a model name. Here are the following
available constructors.
constructor
Create(ASetup: TMappingSetup);
overload
;
constructor
Create(
const
ModelName:
string
);
overload
;
To create a mapping explorer based on a mapping setup, just pass the setup to the constructor (
check here to learn how to create mapping setups)
MyExplorer := TMappingExplorer.Create(MyMappingSetup); or, alternatively, you can just pass the model name. The explorer will only consider all entities belonging to the specified model:
MyExplorer := TMappingExplorer.Create( 'Sample' );
Note that you are responsible to destroy the TMappingExplorer instance you create explicitly.
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5.4
Mapping Setup
Aurelius uses the mapping you have done to manipulate the objects. You do the mapping at design-time (adding attributes to your classes and class members), but this information is of course retrieved at run-time by Aurelius and is cached for better performance. This cached information is kept in an object of class
. Whenever a
object is created to manipulate the objects, a TMappingExplorer object must be provided to it, in order for the object manager to retrieve meta information about the mapping (or the default TMappingExplorer instance will be used).
To create a TMappingExplorer object explicitly, you can pass an instance of a
TMappingSetup object.
So the order of "injection" of objects is illustrated below:
TMappingSetup -> TMappingExplorer -> TObjectManager
The following topics explain different ways of specifying the mapping setup and what custom settings you can do with mapping.
Note that
using Model attribute is a much easier way to create multi-model
Aurelius applications when compared to mapping setup. Check the
topic to learn more about it.
Default Mapping Setup Behavior
5.4.1
Defining a Mapping Setup
To have full control over the mapping setup, the overall behavior is the following.
1. Create and configure a TMappingSetup object
2. Create a TMappingExplorer object passing the TMappingSetup instance
3. Destroy the TMappingSetup object. Keep the TMappingExplorer instance
4. Create several
TObjectManager instances passing the TMappingExplorer
object
5. Destroy the TMappingExplorer object at the end of your application (or when all TObjectManager objects are destroyed and you have finished using Aurelius objects)
The concept is that you obtain a TMappingExplorer object that contains an immutable cache of the mapping scheme, using some initial settings defined in
TMappingSetup. Then you keep the instance of that TMappingeExplorer during the lifetime of the application, using it to create several object manager instances.
Sample code:
uses
Aurelius.Mapping.Setup,
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Aurelius.Mapping.Explorer,
Aurelius.Engine.ObjectManager;
{...}
var
MapSetup: TMappingSetup;
begin
MapSetup := TMappingSetup.Create;
try
// Configure MapSetup object
{..}
// Now create exporer based on mapping setup
FMappingExplorer := TMappingExplorer.Create(MapSetup);
finally
MapSetup.Free;
end
;
// Now use FMappingExplorer to create instances of object manager
FManager := TObjectManager.Create(MyConnection,
FMappingExplorer);
try
// manipulate objects using the manager
finally
FManager.Free;
end
;
// Don't forget to destroy FMappingExplorer at the end of application
end
;
5.4.2
Default Mapping Setup Behavior
In most situations, you as a programmer don't need to worry about manually
. This is because Aurelius provide some default settings and efault instances that makes it transparent for you (and also for backward compatibility).
There is a global TMappingExplorer object available in the following class function:
class function
TMappingExplorer.DefaultInstance:
TMappingExplorer; that is lazily initialized that is used by Aurelius when you don't explicitly define a TMappingExplorer to use. That's what makes you possible to instantiate
objects this way:
Manager := TObjectManager.Create(MyConnection);
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the previous code is equivalent to this:
Manager := TObjectManager.Create(MyConnection,
TMappingExplorer.DefaultInstance);
Note that the TMappingSetup object is not specified here. It means that the
TMappingExplorer object initially available in TMappingExplorer.DefaultInstance
internally uses an empty TMappingSetup object. This just means that no customization in the setup was done, and the default mapping (and all the design-time mapping done by you) is used normally.
If you still want to define a custom mapping setup, but you don't want to create all your object manager instances passing a new explorer, you can alternatively change the TMappingExplorer.DefaultInstance. This way you can define a custom setup, and from that point, all TObjectManager objects to be created without an explicit TMappingExplorer parameter will use the new default instance. The following code illustrates how to change the default instance:
uses
Aurelius.Mapping.Setup,
Aurelius.Mapping.Explorer,
Aurelius.Engine.ObjectManager;
{...}
var
MapSetup: TMappingSetup;
begin
MapSetup := TMappingSetup.Create;
try
// Configure the mapping setup
// Replace default instance of TMappingExplorer
// MAKE SURE that no TObjectManager instances are alive using the old DefaultInstance
TMappingExplorer.ReplaceDefaultInstance(TMappingExplorer.Cre
ate(MapSetup));
finally
MapSetup.Free;
end
;
FManager := TObjectManager.Create(MyConnection);
try
// manipulate objects using the manager
finally
FManager.Free;
end
;
// No need to destroy the old or new default instances.
Aurelius will manager them.
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;
Please attention to the comment in the code above. Make sure you have no existing TObjectManager instances that uses the old TMappingExplorer instance being replaced. This is because when calling ReplaceDefaultInstance method, the old default instance of TMappingExplorer is destroyed, and if there are any TObjectManager instances referencing the destroyed explorer, unexpected behavior might occur.
Nevertheless, you would usually execute such example code above in the beginning of your application.eu
5.4.3
Mapped Classes
By default, TMS Aurelius maps all classes in the application marked with
attribute. Alternatively, you can manually define which class will be mapped in each mapping setup. This allows you to have a differents set of classes for each database connection in the same application. For example, you can have classes A, B and C mapped to a SQL Server connection, and classes D and E mapped to a local SQLite connection.
Defining mapped classes
Mapped classes are defined using TMappingSetup.MappedClasses property.
This provides you a TMappedClasses class which several methods and properties to define the classes to be mapped.
uses
Aurelius.Mapping.Setup,
Aurelius.Mapping.Explorer,
Aurelius.Mapping.MappedClasses,
Aurelius.Engine.ObjectManager;
{...}
var
MapSetup1: TMappingSetup;
MapSetup2: TMappingSetup;
begin
MapSetup1 := TMappingSetup.Create;
MapSetup2 := TMappingSetup.Create;
try
MapSetup1.MappedClasses.RegisterClass(TCustomer);
MapSetup1.MappedClasses.RegisterClass(TCountry);
MapSetup2.MappedClasses.RegisterClass(TInvoice);
FMappingExplorer1 := TMappingExplorer.Create(MapSetup1);
FMappingExplorer2 := TMappingExplorer.Create(MapSetup2);
finally
MapSetup.Free;
end
;
// FManager1 will connect to SQL Server and will only deal with entity classes TCustomer and TCountry
FManager1 := TObjectManager.Create(MySQLServerConnection,
FMappingExplorer1);
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// FManager2 will connect to SQLite and will only deal with entity classe TInvoice
FManager2 := TObjectManager.Create(MySQLiteConnection,
FMappingExplorer2);
// Don't forget to destroy FMappingExplorer1 and
FMappingExplorer2 at the end of application
end
;
Default behavior
You don't need to manually register classes in MappedClasses property. If it is empty, Aurelius will automatically register all classes in the application marked with the
Methods and properties
The following methods and properties are available in TMappedClasses class.
procedure
RegisterClass(Clazz: TClass);
Registers a class in the mapping setup.
procedure
RegisterClasses(AClasses: TEnumerable<TClass>);
Register a set of classes in the mapping setup (you can pass a TList<TClass> or any other class descending from TEnumerable<TClass>.
procedure
Clear;
Unregister all mapped classes. This returns to the default state, where all classes marked with Entity attribute will be registered.
function
IsEmpty: boolean;
Indicates if there is any class registered as a mapped class. When IsEmpty returns true, it means that the default classes will be used (all classes marked with Entity attribute).
property
Classes: TEnumerable<TClass>
read
GetClasses;
Lists all classes currently registered as mapped classes.
procedure
UnregisterClass(Clazz: TClass);
Unregister a specified class. This method is useful when combined with
GetEntityClasses. As an example, the following will register all classes marked with Entity attribute (the default classes), except TInternalConfig:
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MapSetup.MappedClasses.RegisterClasses(TMappedClasses.GetEntityC
lasses);
MapSetup.MappedClasses.UnregisterClass(TInternalConfig);
class function
GetEntityClasses: TEnumerable<TClass>;
class function
GetDefaultClasses: TEnumerable<TClass>;
class function
GetModelClasses(
const
ModelName:
string
):
TEnumerable<TClass>;
Helper functions that return classes in the application marked with
attribute. You can call GetModelClasses to retrieve entity classes belonging to the model specified by ModelName. You can call GetDefaultClasses to retrieve entity classes belonging to the default model (either classes with no Model attribute or belonging to model "Default"). Or you can use GetEntityClasses to retrieve all entity classes regardless of the model they belong to. This is not a list of the currently mapped classes (use Classes property for that). This property is just a helper property in case you want to register all classes marked with Entity attribute and then remove some classes. It's useful when used together with UnregisterClass method. Note that if ModelName is empty string when calling GetModelClasses, model will be ignored and all classes marked with
Entity attribute, regardless of the model, will be retrieved.
Calling GetModelClasses('') is equivalent to calling GetEntityClasses.
Calling GetModelClasses(TMappedClasses.DefaultModelName) is equivalent to calilng GetDefaultClasses.
5.4.4
Dynamic Properties
Dynamic properties are a way to define mapping to database columns at runtime. Regular mapping is done as following:
[Column( 'MEDIA_NAME' , [TColumnProp.Required], 100 )]
property
MediaName:
string read
FMediaName
write
FMediaName;
But what if don't know at design-time if the MEDIA_NAME column will be available in the database? What if your application runs in many different customers and the database schema in each customer is slightly different and columns are not known at design-time? To solve this problem, you can use dynamic properties, which allows you to manipulate the property this way:
MyAlbum.CustomProps[ 'MediaName' ] := 'My media name' ;
The following steps describe how to use them:
Preparing Class for Dynamic Properties
Registering Dynamic Properties
Dynamic Properties in Queries and Datasets
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5.4.4.1
Preparing Class for Dynamic Properties
To make your class ready for dynamic properties, you must add a new property that will be used as a container of all dynamic properties the object will have.
This container must be managed (created and destroyed) by the class and is an object of type TDynamicProperties:
uses
Aurelius.Mapping.Attributes,
Aurelius.Types.DynamicProperties,
type
[Entity]
[Automapping]
TPerson =
class private
FId: integer;
FName:
string
;
FProps: TDynamicProperties;
public constructor
Create;
destructor
Destroy;
override
;
property
Id: integer
read
FId
write
FId;
property
Name:
string read
FName
write
FName;
property
Props: TDynamicProperties
read
FProps;
end
;
constructor
TPerson.Create;
begin
FProps := TDynamicProperties.Create;
end
;
destructor
TPerson.Destroy;
begin
FProps.Free;
inherited
;
end
;
The
Automapping attribute is being used in the example, but it's not required to
use dynamic properties. You just need to declare the TDynamicProperties property, with no attributes associated to it.
5.4.4.2
Registering Dynamic Properties
Dynamic properties must be registered at run-time. To do that, you need to use a custom
mapping setup . You need to create a TMappingSetup object,
register the dynamic properties using DynamicProps property, and then
create a TMappingExplorer object from this setup to be used when creating
TObjectManager instances, or just
TMappingExplorer.DefaultInstance
The DynamicProps property is an indexed property which index is the class where the dynamic property will be registered. The property returns a
TList<TDynamicProperty> which you can use to manipulate the registered dynamic properties. You don't need to create or destroy such list, it's managed
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by the TMappingSetup object. You just add TDynamicProperty instances to it, and you also don't need to manage such instances.
The following code illustrates how to create some dynamic properties in the
class TPerson we created in the topic " Preparing Class for Dynamic Properties ".
uses
{...}
, Aurelius.Mapping.Setup;
procedure
TDataModule1.CreateDynamicProps(ASetup:
TMappingSetup);
var
PersonProps: TList<TDynamicProperty>;
begin
PersonProps := ASetup.DynamicProps[TPerson];
PersonProps.Add(
TDynamicProperty.Create( 'Props' , 'HairStyle' ,
TypeInfo(THairStyle),
TDynamicColumn.Create( 'HAIR_STYLE' )));
PersonProps.Add(
TDynamicProperty.Create( 'Props' , 'Photo' , TypeInfo(TBlob),
TDynamicColumn.Create( 'PHOTO' )));
PersonProps.Add(
TDynamicProperty.Create( 'Props' , 'Extra' , TypeInfo(
string
),
TDynamicColumn.Create( 'COL_EXTRA' , [], 30 )));
end
;
procedure
TDataModule1.DefineMappingSetup;
var
MapSetup: TMappingSetup;
begin
MapSetup := TMappingSetup.Create;
try
CreateDynamicProps(MapSetup);
TMappingExplorer.ReplaceDefaultInstance(TMappingExplorer.Cre
ate(MapSetup));
finally
MapSetup.Free;
end
;
end
;
In the previous example, we have registered three dynamic properties in class
TPerson:
- HairStyle, which is a property of type THairStyle (enumerated type) and will be saved in database column HAIR_STYLE
- Photo, a property of type TBlob, to be saved in column PHOTO
- Extra, a property of type string, to be saved in column COL_EXTRA, size 30.
Note that the type of dynamic property must be informed. It should be the type of the property (not the type of database column) as if the property was a real property in the class. You can create dynamic properties of any type supported by Aurelius, with two exceptions:
associations are not supported
(and such Proxy types are not allowed) and
types are also not
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supported, but because they are not needed. All dynamic properties are nullable because
they are in essence TValue types and you can always set
them to TValue.Empty values (representing a null value).
The first parameter of TDynamicProperty.Create method must have the name of the TPerson property which will hold the dynamic property values (we have created a property Props of type TDynamicProperties in class TPerson).
Declaration of TDynamicProperty and TDynamicColumn objects are as following:
TDynamicProperty =
class public constructor
Create(AContainerName, APropName:
string
;
APropType: PTypeInfo; ColumnDef: TDynamicColumn);
destructor
Destroy;
override
;
function
Clone: TDynamicProperty;
property
ContainerName:
string read
FContainerName
write
FContainerName;
property
PropertyName:
string read
FPropertyName
write
FPropertyName;
property
PropertyType: PTypeInfo
read
FPropertyType
write
FPropertyType;
property
Column: TDynamicColumn
read
FColumn
write
FColumn;
end
;
TDynamicColumn =
class public constructor
Create(Name:
string
);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps;
Length: Integer);
overload
;
constructor
Create(Name:
string
; Properties: TColumnProps;
Precision, Scale: Integer);
overload
;
function
Clone: TDynamicColumn;
property
Name:
string read
FName
write
FName;
property
Properties: TColumnProps
read
FProperties
write
FProperties;
property
Length: integer
read
FLength
write
FLength;
property
Precision: integer
read
FPrecision
write
FPrecision;
property
Scale: integer
read
FScale
write
FScale;
end
;
Note that the overloaded Create methods of TDynamicColumn are very similar to the ones used in
Column attribute . The TDynamicColumn represents contains
info about the physical table column in the database where the dynamic property will be mapped to, and its properties behave the same as the ones described in the documentation of
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5.4.4.3
Using Dynamic Properties
Once you have
prepared your class for dynamic properties , and registered the dynamic properties
in the mapping setup, you can manipulate the properties as any other property of your object, using the TDynamicProperties container object. It's declared as following:
TDynamicProperties =
class public property
Prop[
const
PropName:
string
]: TValue
read
GetItem
write
SetItem;
default
;
property
Props: TEnumerable<TPair<
string
, TValue>>
read
GetProps;
end
;
This is how you would use it:
Person := Manager.Find<TPerson>(PersonId);
Person.Props[ 'Extra' ] := 'Some value' ;
Manager.Flush;
ExtraValue := Person.Props[ 'Extra' ];
Note that in the example above, the dynamic property behave exactly as a regular property. The Flush method have detected that the "Extra" property was changed, and will update it in the database accordingly.
Be aware that Props type is TValue, which is a generic container. Some implicit conversions are possible, as illustrated in the previous example using the dynamic property "Extra". However, in some cases (and to be safe you can use this approach whenever you are not sure about using it or not) you will need to force the TValue to hold the correct type of the property. The following example shows how to define a value for the dynamic property HairStyle, which was registered as the type THairStyle (enumerated type):
Person := TPerson.Create;
Person.Props[ 'HairStyle' ] :=
TValue.From<THairStyle>(THairStyle.Long);
Manager.Save(Person);
PersonHairStyle := Person.Props[ 'HairStyle' ].AsType<THairStyle>;
The same applies to blob properties, which must be of type
var
Blob: TBlob;
begin
// Saveing a blob
Blob.LoadFromStream(SomeStream);
Person.Props[ 'Photo' ] := TValue.From<TBlob>(Blob);
Manager.SaveOrUpdate(Person);
// Reading a blob
Blob := Person.Props[ 'Photo' ].AsType<TBlob>;
Blob.SaveToStream(MyStream);
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Dynamic blob properties can also be
lazy-loaded just as any regular blob
property.
5.4.4.4
Dynamic Properties in Queries and Datasets
When it comes to
, dynamic properties behave exactly as regular properties. In queries, they are accessed by name as any other query.
So for example the following query:
Results := Manager.Find<TPerson>
.Where(
(Linq[ 'HairStyle' ] = THairStyle.Long)
and
Linq[ 'Extra' ].Like( '%value%' )
)
.AddOrder(TOrder.Asc( 'Extra' ))
.List; will list all people with HairStyle equals to Long and Extra containing "value", ordered by Extra. No special treatment is required, and the query doesn't care if HairStyle or Extra are dynamic or regular properties.
The same applies to the TAureliusDataset. The dynamic properties
are initialized in fielddefs as any other property, and can be accessed through
dataset fields:
// DS: TAureliusDataset;
DS.Manager := Manager;
Person := TPerson.Create;
DS.SetSourceObject(Person);
DS.Open;
DS.Edit;
DS.FieldByName( 'Name' ).AsString := 'Jack' ;
DS.FieldByName( 'Extra' ).AsString := 'extra value' ;
// Enumerated types are treated by its ordinal value in dataset
DS.FieldByName( 'HairStyle' ).AsInteger :=
Ord(THairStyle.Short);
BlobField := DS.FieldByName( 'Photo' )
as
TBlobField;
// use
BlobField as usual
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Chapter
VI
Manipulating
Objects
TMS Aurelius Documentation
6
6.1
Manipulating Objects
This chapter explains how to manipulate objects. Once you have properly
connected to the database and configure all mapping between the objects and
the database, it's time for the real action. The following topics explain how to save, update, delete and other topics about dealing with objects. Querying objects using complex criteria and projections is explained in a specific chapter only for
Object Manager
The Object Manager is implemented by the TObjectManager class which is declared in unit Aurelius.Engine.ObjectManager:
uses
{...}
, Aurelius.Engine.ObjectManager;
It's the layer between your application and the database, providing methods for saving, loading, updating, querying objects. It performs
memory management , by controlling objects lifetime cycle, destroying them when they
are not needed anymore, and caching objects by using identity mappings to ensure a single object is not loaded twice in the same manager.
The Object Manager also keeps tracking of changes in objects - you can update the content of objects (change properties, add associations, etc.) and then call Flush method to ask the object manager to update all object changes in the database at once.
The list below is a quick reference for the main methods and properties provided by TObjectManager object. A separate topic is provided for each method listed below:
Creating a new object manager
Directly create a TObjectManager instance, passing the IDBConnection interface that represents a
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Manager := TObjectManager.Create(MyConnection);
try
// perform operations with objects
finally
Manager.Free;
end
; alternatively, you can also pass a
, which holds a
mapping model different than the default.
Manager := TObjectManager.Create(MyConnection,
MyMappingExplorer);
//or
Manager := TObjectManager.Create(MyConnection,
TMappingExplorer.Get( 'MyModel' ));
Save method
Use it to
(insert into database) new entity objects:
Customer := TCustomer.Create;
Customer.Name := 'TMS Software' ;
Manager.Save(Customer);
Update method
Use it to
update an existing object in the database:
Customer := TCustomer.Create;
Customer.Id := 10 ;
Customer.Email := '[email protected]' ;
Manager.Update(Customer);
SaveOrUpdate method
Use it to save or update an object depending on the Id specified in the object
(update if there is an Id, save it otherwise):
Customer.LastName := 'Smith' ;
Manager.SaveOrUpdate(Customer);
Flush method
Commit to the database all changes made to the managed objects.
Customer1 := Manager.Find<TCustomer>( 1 );
Customer2 := Manager.Find<TCustomer>( 2 );
Customer1.Email := '[email protected]' ;
Customer2.City := 'Miami' ;
Manager.Flush;
// Update Customer1 e-mail and Customer2 city in database
Flush method for single entity
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Commit to the database changes made to a single object - it's an overloaded version of Flush method that receives an object:
Customer1 := Manager.Find<TCustomer>( 1 );
Customer2 := Manager.Find<TCustomer>( 2 );
Customer1.Email := '[email protected]' ;
Customer2.City := 'Miami' ;
Manager.Flush(Customer1);
// Update Customer1 e-mail - Customer2 changes are not persisted
Merge method
Use it to
merge a transient object into the object manager and obtain the
persistent object.
Customer := TCustomer.Create;
Customer.Id := 12 ;
Customer.Name := 'New name' ;
ManagedCustomer := Manager.Merge<TCustomer>(Customer);
In the example above, Merge will look in the cache or database for a
TCustomer with id equals to 12. If it's not found, an exception is raised. If found, it will update the cached customer object with the new information and return a reference to the cached object in CachedCustomer. Customer reference will still point to an unmanaged object, so two instances of
TCustomer will be in memory.
Replicate method
The replicate method behaves exactly the same as the
The only difference is that, in the example above, if no Customer with id 12 is found in the database, instead of raising an exception, Replicate will create the new customer with that id.
Find method
Use
Find method to retrieve an object given its Id:
Customer := Manager.Find<TCustomer>(CustomerId);
The id value is a variant type and must contain a value of the same type of the class Identifier (specified with the
Id attribute). For example, if the
identifier is a string type, id value must be a variant containing a string. For classes with
composite id , a variant array of variant must be specified with all
the values of the id fields.
You can alternatively use the non-generic overload of Find method. It might be useful for runtime/dynamic operations where you don't know the object class at the compile time:
Customer := Manager.Find(TCustomer, CustomerId);
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FindAll method
Return all object instances of an specified class in the database. It's equivalent to perform an SELECT statement over a table without any filtering. A
TObjectList<T> is returned.
var
AllCustomers: TObjectList<TCustomer>;
begin
AllCustomers := Manager.FindAll<TCustomer>;
try
{use AllCustomers}
finally
AllCustomers.Free;
end
;
Remove method
Use it to
remove the object from the persistence (i.e., delete it from database
and from object manager cache).
CustomerToRemove := Manager.Find<TCustomer>(CustomerId);
Manager.Remove(CustomerToRemove);
Find<T> method
Use Find<T> to create a new
to find objects based on the specified criteria.
Results := Manager.Find<TTC_Customer>
.Where(Linq[ 'Name' ] = 'Mia Rosenbaum' )
.List;
CreateCriteria<T> method
CreateCriteria is just an alias for Find<T> method. Both are equivalent:
Results := Manager.CreateCriteria<TTC_Customer>
.Where(Linq[ 'Name'] = 'Mia Rosenbaum' )
.List;
Evict method
Use to
evict (dettach) an entity from the manager:
Manager.Evict(Customer);
IsAttached method
Checks if the specified object instance is already attached (persistent) in the object manager.
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Manager.IsAttached(Customer)
then
Manager.Update(Customer);
FindCached<T> method
Use FindCached method to retrieve an object from the manager's cache, given its Id.
Customer := Manager.FindCached<TCustomer>(CustomerId);
This method is similar to Find method but the difference is that if the object is not in manager cache, Aurelius will not hit the database to retrieve the objec instead, it will return nil. Because of that, this method should be used only to check if the object is already in the manager - it's not useful to retrieve data from database.
You can alternatively use the non-generic overload of FindCached method. It might be useful for runtime/dynamic operations where you don't know the object class at the compile time:
Customer := Manager.FindCached(TCustomer, CustomerId);
IsCached<T> method
Checks if an object of the specified class with the specified id is already loaded in the object manager.
if not
Manager.IsCached<TCustomer>(CustomerId)
then
ShowMessage( 'Not loaded' );
You can use the non-generic version as well:
if not
Manager.IsCached(TCustomer, CustomerId)
then
ShowMessage( 'Not loaded' );
OwnsObjects property
If true (default), all managed objects are destroyed when the TObjectManager object is destroyed. If false, the objects remain in memory.
Customer := Manager.Find<TCustomer>(CustomerId);
Manager.OwnsObjects := false;
Manager.Free;
// Customer object is still available after Manager is destroyed
ProxyLoad and BlobLoad methods
use to load a proxy object (or blob) based on meta information (see
for more information)
function ProxyLoad(ProxyInfo: IProxyInfo): TObject;
function BlobLoad(BlobInfo: IBlobInfo): TArray<byte>;
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6.2
UseTransactions property
When true, all internal operations peformed by the object manager (Save,
Update, Merge, Remove, etc.) as enclosed between transactions (it means if no transaction is active, the manager will create one just for the operation, then later commit). This is needed because even a single manager operation can perform several SQL statements in the database (due to cascades for example).
If false, the manager won't create new transactions, and it's up to you to make sure that a transaction is active, otherwise if the internal process fails, some records might become updated in the database, while others don't.
The default value of this property is controlled globally by the
Memory Management
Entity objects are saved and loaded to/from database using a TObjectManager object, which provides methods and properties for such operations. All entity objects cached in TObjectManager are managed by it, and you don't need to free such objects (unless you set OwnsObjects property to False). Also, entity objects retrieved from database, either loading by identifier or using queries, are also managed by the TObjectManager.
Concept of object state
In Aurelius when an object is told to be persistent (or cached, or managed) it means that the TObjectManager object is aware of that object and is
"managing" it. When TObjectManager loads any object from the database, the object instances created in the loading process are persistent. You can also turn objects into persistent object when you for example call Save, Update or
Merge methods.
When the TObjectManager is not aware of the object, the object is told to be
transient (or uncached, or unmanaged).
Don't confuse a transient object with an object that is not saved into the database yet. You might have a TCustomer object which has been already saved in the database, but if the TCustomer instance you have is not being managed by the TObjectManager, it's transient.
Also, don't confuse persistent with saved. A persistent object means that
TObjectManager is aware of it and it's managing it, but it might not be saved to the database yet.
Object lists
It's important to note that when retrieving object lists from queries, the list itself must be destroyed, although the objects in it are not. Note that when you use projections in queries, the objects returned are not entity objects, but result objects. In this case the objects are not managed by the object
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manager, but the list retrieved in result queries have their OwnsObjects set to true, so destroying the list will destroy the objects as well.
Unique instances
When dealing with entity objects (saving, loading, querying, etc.), object manager keeps an internal Identity Map to ensure that only one instance of each entity is loaded in the TObjectManager object. Each entity is identified by it's Id attribute. So for example, if you execute two different queries using the same object manager, and the query returns the same entity (same id) in the queries, the object instance in the both queries returned will be the same. The object manager will not create a different object instance every time you query the object. If you use a different TObjectManager object for each query, then you will have different instances of the same entity object
Examples
The code snippets below illustrates several the different situations mentioned above.
Saving objects
Customer := TTC_Customer.Create;
Customer.Name := 'Customer Name' ;
ObjectManager1.Save(Customer);
// From now on, you don't need to destroy Customer object anymore
// It will be destroyed when ObjectManager1 is destroyed
Loading objects
Customer := Manager1.Find<TCustomer>(CustomerId);
Customer2 := Manager1.Find<TCustomer>(CustomerId);
// Since CustomerId is the same for both queries, the same instance will be
// returned in Customer and Customer2 (Customer = Customer2), and you don't
// need to destroy such instance, it's manager by Manager1.
Retrieving entities from queries
Results := Manager.Find<TCustomer>
.Add(Linq[ 'Name'] = 'TMS Software' )
.List;
Results.Free;
// Results is a TObjectList<TCustomer> object that needs to be destroyed
// However, the object instances it holds are not destroyed and are kept
// in Manager cache. The instances are also ensured to be unique in Manager context
Retrieving projected query results
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6.3
Results := Manager.Find<TTC_Estimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ))
.Add(TProjections.Group( 'c.Name' ))
)
.ListValues;
Results.Free;
// In this case the query does not return entity objects, but result objects (TCriteriaResult)
// Such result objects are not managed by TObjectManager.
However, in this case,
// The Results object list is returned with its OwnsObjects property set to true. Thus, when
// you destroy Results object, the TCriteriaResult objects it holds will also be destroyed.
Using unmanaged objects
If for some reason you want to keep object instances available even after the object manager is destroyed (for example, after a query, you want to destroy object manager but keep the returned objects in memory), then just set the
TObjectManager.OwnsObjects property to false:
Manager.OwnsObjects := false;
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ] = 'TMS Software' )
.List;
Manager.Free;
// Now although Manager object was destroyed, all objects in
Results list will be kept in memory,
// EVEN if you destroy Results list itself later.
Saving Objects
Using TObjectManager you can save (insert) objects using Save method. It is analog to SQL INSERT statement - it saves the object in database.
Customer1 := TCustomer.Create;
Customer1.Name := 'John Smith' ;
Customer1.Sex := tsMale;
Customer1.Birthday := EncodeDate( 1986 , 1 , 1 );
Manager1.Save(Customer1);
The identifier of the object (mapped using
attribute) must not have a value, otherwise an exception will be raised - unless the generator defined in Id attribute is TIdGenerator.None. In this case, you must manually provide the id value of the object, and so of course Aurelius will accept an object with an id value. But you must be sure that there are no objects in the database with the same id value, to avoid duplicate values in the primary key.
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6.4
When saving an object, associations and items in collections might be saved as well, depending on how cascade options are set when you defined the
ManyValuedAssociation attribute. In the example below,
customer is defined to have SaveUpdate cascade. It means that when invoice is saveed, the customer is saved as well, before the invoice.
Customer := TTC_Customer.Create;
Customer.Name := 'Customer Name' ;
Invoice := TTC_Invoice.Create;
Invoice.InvoiceType := 999 ;
Invoice.InvoiceNo := 123456 ;
Invoice.Customer := Customer;
Invoice.IssueDate := Date;
Manager1.Save(Invoice);
You can also use SaveOrUpdate method to save objects. The difference from
Save is that if the object has an id value set, SaveOrUpdate will internally call
Update method instead of Save method. So, if you use TIdGenerator.None in the
Id attribute of your object class, SaveOrUpdate will not work.
Updating Objects - Flush
You modify objects using the
TObjectManager method Flush. The state of all
objects persisted in object manager is tracked by it. Thus, if you change any property of any object after it's loaded by the database, those changes will be updated to the database when Flush method is called. Consider the example below:
Customer1 := Manager1.Find<TCustomer>(CustomerId);
Customer1.Email := '[email protected]' ;
Customer2 := Manager1.Find<TCustomer>(Customer2Id);
Customer2.Email := '[email protected]' ;
Manager1.Flush;
The Flush method will detect all objects which content has been changed since they were loaded, and then update them all in the database. In the example above, both customers 1 and 2 will have their e-mail changed.
It's possible that, by any reason, you want to update a detached object, in other words, an object that is not being tracked (persisted) by the manager.
This might happen, for example, if you loaded an object with the manager, then destroyed the manager but kept the object reference (using
TObjectManager.OwnsObjects = false). Or, for example, if you created the object instance yourself, and set its id property to a valid value. In this case the object is not in the manager, but you want to update the database using the object you have.
In this case, you can use Update method. This method will just take the passed transient instance and attach it to the TObjectManager. Then when you later call Flush, the changes will be persisted to the database. Note that when you call Update, no data is retrieved from the database. This means that the object manager doesn't know the original state of the object (data saved in database). The consequence is that all properties of the object passed to
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Update method will later be saved to the database when Flush is called. So you must be sure that all the persistent properties of the object have the correct value to be saved to the database.
Customer2 := Manager1.Find<TCustomer>(Customer2Id);
Manager1.OwnsObjects := false;
Manager1.Free;
Customer2.Name := 'Mary' ;
Customer2.Sex := tsFemale;
Manager2.Update(Customer2);
Manager2.Flush;
In the example above, a TCustomer object was loaded in Manager1. It's not attached to Manager2. When Update method is called in Manager2, all data in
Customer2 object will be updated to the database, and it will become persistent in Manager2.
The cascades defined in
Association attributes in your class are applied here.
Any associated object or collection item that has TCascadeType.SaveUpdate
defined will also be updated in database.
Merging
If you call Update method passing, say, Object1, but there was already another object attached to the TObjectManager with the same id (Object2), an exception will be raised. In this case, you can use
transient object ("outside" the manager) into a persistent object ("inside" the manager).
Flushing a single object
Calling Flush might be slow if you have many entities in the manager. Flush will iterate through all entities and check if any of them is modified - and persist changes to the database. Alternatively, you can flush a single entity by using an overloaded version of Flush that receives a single object:
Customer1 := Manager1.Find<TCustomer>(CustomerId);
Customer1.Email := '[email protected]' ;
Customer2 := Manager1.Find<TCustomer>(Customer2Id);
Customer2.Email := '[email protected]' ;
Manager1.Flush(Customer1);
In the example above, only changes made to Customer1 will be persisted.
Customer2 changes will still be in memory only, and you would have to call
Flush or Flush(Customer2) to persist the changes. This gives you finer control over what should be persisted and helps you increase performance of your code.
You must be careful, though, about associated objects. When you call Flush without specifying an object you are safe that all changes in the manager are persisted. You flushing a single object, associated objects might be flushed or not, depending on how the cascade options are set for that
Many-Valued Association ). If the association includes the TCascadeType.Flush,
then it will also be flushed.
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6.5
Merging/Replicating Objects
When you use
method in a
TObjectManager object, there should be no
managed object with same Id in the object manager, otherwise an exception is raised. You can avoid such exception using the Merge or Replicate methods.
These methods behave almost exactly the same, and will take a transient instance and merge it into the persistent instance. In other words, all the content of the transient object will be copied to the persistent object. Note that the transient object will continue to be transient.
If there is no persistent object in the object manager with the same id, the object manager will load an object from the database with the same id of the transient object being merged.
If the object has an id and no object is found in the database with that id, the behavior depends on the method called (and that is the only difference between Merge and Replicate methods):
- if Merge method was called, an exception will be raised;
- if Replicate method was called, a new object with the specified id will be saved (inserted).
Customer2 := TCustomer.Create;
Customer2.Id := Customer2Id;
Customer2.Name := 'Mary' ;
Customer2.Sex := tsFemale;
MergedCustomer := Manager2.Merge<TCustomer>(Customer2);
Manager2.Flush;
In the example above, a TCustomer object was created and assigned an existing id. When calling Merge method, all data in Customer2 will be copied to the persistent object with same id in Manager2. If no persistent object exists in memory, it will be loaded from the database. Customer2 variable will still reference a transient object. The result value of Merge/Replicate method is a reference to the persistent object in the object manager.
If the transient object passed to Merge/Replicate has no id, then a Save operation takes place. Merge/Replicate will create a new internal instance of object, copy all the contents from the passed object to the internal one, and
Save (insert) the newly created object. Again, the object returned by Merge/
Replicate is different from the one passed. Take a look at the following example:
NewCustomer := TCustomer.Create;
NewCustomer.Name := 'John' ;
MergedCustomer := Manager2.Replicate<TCustomer>(NewCustomer);
// MergedCustomer <> NewCustomer! NewCustomer must be destroyed
In the example above, NewCustomer doesn't have an id. In this case, Merge/
Replicate will create a new customer in database, and return the newly created object. MergedCustomer points to a different instance than NewCustomer.
MergedCustomer is the persistent one that is tracked by the object manager
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(and will be destroyed by it when manager is destroyed). NewCustomer continues to be a transient instance and must be manually destroyed.
Note that Merge/Replicate does nothing in the database in update operations it just updates the persistent object in memory. To effectively
in the database you should then call Flush method. The only exception is the one described above when the object has no id, or when Replicate saves a new object with existing id. In those cases, a Save (insert) operation is performed immediately in the database.
The cascades defined in
attributes in your class are applied here. Any associated object or collection item that has
TCascadeType.Merge defined will also be merged/replicated into the manager and the reference will be changed. For example, if Customer has a Country property pointing to a transient TCountry object. The TCountry object will me merged, a new instance will be returned from the merging process, and
Customer.Country property will be changed to reference the new instanced returned by the merging process.
6.6
6.7
Removing Objects
You can remove an object from the database using Remove method from a
object. Just pass the object that you want to destroy. The object must be attached to the object manager.
Customer1 := Manager1.Find<TCustomer>(CustomerId);
Manager1.Remove(Customer1);
The cascades defined in
attributes in your class are applied here. Any associated object or collection item with delete cascade will also be removed from database.
Finding Objects
You can quickly find (load) objects using Find method of
just need to pass the Id of the object, and object manager will retrieve the instance of the object loaded in memory. If the object is not attached to the object manager (not in memory), then it tries to load the object from database. If there is no object (record) in the database with that Id, it returns nil.
Customer1 := Manager1.Find<TCustomer>(CustomerId);
// Customer1 has an instance to the loaded customer object.
The associations will be loaded depending on how the fetch mode was defined in
Association attribute. They will be loaded on the fly or on demand,
depending if they are set as
lazy-loaded associations or not.
If you want to retrieve several objects of a class from the database using some criteria (filtering, ordering), just use Find without parameter, it will return
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6.8
a Criteria object which you can use to add filters, ordering and later retrieve the results:
var
Customers: TList<TCustomer>;
begin
Customers := Manager1.Find<TCustomer>.List;
// Take just the first 10 customers ordered by name
Customers :=
Manager1.Find<TCustomer>.Take( 10 ).OrderBy( 'Name' ).List;
Aurelius is very powerful on querying capabilities. There is a full chapter explaining how to perform
Refreshing Objects
You can refresh an object using Refresh method from a
object. Just pass the object that you want to refresh. The object must be attached to the object manager.
Manager1.Refresh(Customer1);
Refresh method performs operates almost the same way as
method. The main difference is that Find method only create new instances that don't exist in the manager and if the instance already exists, it's left untouched. Refresh method, instead, will perform the SELECT statement in the database no matter what, and if the instances already exist in manager, it will update its properties and associations with data retrieved from the database, discarding the existing values in memory, if different.
Note existing transient associations will NOT be destroyed. For example, consider the following code:
Customer1 := Manager.Find<TCustomer>( 1 );
NewCountry := TCountry.Create;
Customer1.Country := NewCountry;
Manager.Refresh(Customer1);
In the code above a TCustomer instance is loaded from the database, and its
Country property is updated to point to a transient TCountry reference. When
Refresh method is called, Customer1 properties will be reloaded from the database, and thus Country property will point again to the original TCountry instance in the manager (or nil if there is no country associated with he customer). However, the instance referenced by NewCountry will not be destroyed. It's up to you to destroy the transient instances unreferenced by
Refresh method.
The cascades defined in
attributes in your class are applied here. Any associated object or collection item with
Refresh cascade will also have its properties refreshed.
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6.9
Evicting Objects
In some situations you want to remove (dettach) an object from the
, but without deleting it from database (so you can't use
Remove method) and without destroying the instance.
To do that, you can use Evict method. Just pass the object that you want to evict. If the object is not attached to the manager, no operation is performed.
Manager1.Evict(Customer1);
The cascades defined in
attributes in your class are applied here. Any associated object or collection item with cascade option including TCascadeType.Evict will also be evicted (dettached) from the manager.
Note that since the object is not in the manager anymore, you must be sure to destroy it (unless of course you attach it to another manager using for example
Update method). Also pay attention to associated objects. If
TCascadeType.Evict is defined for associated objects, they will also be evicted and must be destroyed as well.
6.10
Transaction Usage
You can use transactions when
manipulating objects , so that you make sure all
operations under the transaction are performed successfully (commit) or anything is reverted (rollback). Usage is simple and is done pretty much the same way you would do when accessing a database in a traditional way.
The transactions are started under the
IDBConnection interface context. You
can start a transaction using IDBConnection.BeginTransaction method, which will return a IDBTransaction interface. The IDBTransaction in turn has only two methods: Commit and Rollback.
uses
{...}
, Aurelius.Drivers.Interfaces;
var
Transaction: IDBTransaction;
begin
Transaction := Manager.Connection.BeginTransaction;
try
{ Perform manager operations}
Transaction.Commit;
except
Transaction.Rollback;
raise
;
end
;
end
;
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Transactions in Aurelius can be nested. This means that if a transaction was already started in IDBConnection but not commited or rolled back yet, creating a new transaction and commiting or rolling it back has no effect. For example:
OuterTransaction := Manager.Connection.BeginTransaction;
InnerTransaction := Manager.Connection.BeginTransaction;
InnerTransaction.Commit;
// This has NO effect, the same for rollback.
OuterTransaction.Commit;
// Commit (or Rollback) is effectively performed here
6.11
Concurrency Control
When working with multiple users/clients, it might be possible that two or more users try to change the same entity (records in database). TMS Aurelius provides some mechanisms to avoid problems in those situations.
Changed fields
When
updating objects , Aurelius detects which property have changed since
the entity was loaded from the database in the manager, and it only updates those columns in the database. For example, suppose two users load the same
TCustomer (with same id) from the database at the same time:
// User1
User1Customer := Manager1.Find<TCustomer>( 1 );
// User2
User2Customer := Manager2.Find<TCustomer>( 1 );
Now first user changes customer's city and update, and second user changes customer's document and update:
// User1
User1Customer.City := 'New City' ;
Manager1.Flush;
// User2
User2Customer.Document := '012345' ;
Manager2.Flush;
Here are the SQL executed by Aurelius for each user (SQL were simplified for better understanding, the actual SQL uses parameters):
User1:
Update Customer
Set City = 'New City'
Where Id = 1
User2:
Update Customer
Set Document = '012345'
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Where Id = 1
Even if TCustomer class has lots of customer, and some properties might be outdated in memory, it doesn't cause any trouble or data loss here, because only changed data will be commited to the database. In the end, the
TCustomer object in database will have both the new city and new document correct.
This is a basic mechanism that solves concurrency problems in many cases. If it's not enough, you can use entity versioning.
Entity Versioning
It might be possible that two users change the exactly same property, in this case, one of the users will "lose" their changes, because it will be overwritten by the other user. Or some other types of operations are performed where all fields are updated (when entity is put in manager without being loaded from database for example, so the manager can't tell which properties were changed).
Or maybe you just need to be sure that the object being updated needs to hold the very latest data. A typical case is where you are updating account balance or inventory records, so you increment/decrement values and need to ensure that no other user changed that data since you loaded.
In this case, you can use entity versioning. To accomplish this, you just need to create an extra integer property in the class, map it (so it's persisted in database) and add the [Version] attribute to it:
[Entity, Automapping]
TCustomer =
class private
FId: Integer;
FName:
String
;
{...}
[Version]
FVersion: Integer;
{...}
end
;
And that's it. Once you do this, Aurelius will make sure that if you update (or delete) an entity, data it holds is the very latest one. If it's not, because for example another user changed the database record in the meanwhile, an exception will be raised and then you can decide what to do (refresh the object for example).
Let's take a look at how it works. First, two users load the same object at the same time:
// User1
User1Customer := Manager1.Find<TCustomer>( 1 );
// User1Customer.Version is 1
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// User2
User2Customer := Manager2.Find<TCustomer>( 1 );
// User1Customer.Version is 1
Then User1 updates customer:
User1Customer.City := 'New City' ;
User1Customer.Flush;
// User1Customer.Version becomes 2 (also in database)
This is the SQL executed by Aurelius:
Update Customer
Set City = 'New City', Version = 2
Where Id = 1 and Version = 1
Record is changed successfully because the current version in database is 1, so the actual record is updated.
Now, if User2 tries to update the old customer:
// User2Customer.Version is still 1!
User2Customer.City := 'Another city' ;
User2Customer.Flush;
Aurelius tries to execute the same SQL:
Update Customer
Set City = 'Another City', Version = 2
Where Id = 1 and Version = 1
However this will fail, because the version in the database is not 1 anymore, but 2. Aurelius will detect that no records were affected, and will raise an
EVersionedConcurrencyControl exception.
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Chapter
VII
Queries
TMS Aurelius Documentation
7
7.1
Queries
You can perform queries with Aurelius, just like you would do with SQL statements. The difference is that in Aurelius you perform queries at object level, filtering properties and associations. Most classes you need to use for querying are declared in unit Aurelius.Criteria.Base.
Creating Queries
Queries are represented by an instance of TCriteria object. To execute queries, you just create an instance of TCriteria object, use its methods to add
projections , etc., and then call List method to execute the
query and retrieve results.
Create a new query (TCriteria instance)
Use either Find<T>, CreateCriteria<T> or CreateCriteria method of a
instance to create a new query instance. You must always define the class which you want to search objects for:
MyCriteria := Manager1.CreateCriteria(TCustomer); or the recommended generic version, which will return a TCriteria<T> object:
MyCriteria := Manager1.Find<TCustomer>;
MyCriteria := Manager1.CreateCriteria<TCustomer>;
Memory management
One important thing you should know: the TCriteria object instance is automatically destroyed when you
retrieve query results , either using List,
ListValues, UniqueResult or UniqueValue methods. This is done this way so it's easier for you to use the
fluent interface , so you don't need to keep instances
to objects in variables and destroy them.
So be aware that you don't need to destroy the TCritera object you created using CreateCriteria or Find, unless for some reason you don't retrieve the query results.
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If you don't want this behavior to apply and you want to take full control over the TCriteria lifecycle (for example, you want to keep TCriteria alive for some time to add more filters programatically), you can set TCriteria.AutoDestroy
property to false (it's true by default). This way TCriteria will not be destroyed automatically and you must destroy it at some point:
MyCriteria := Manager1.CreateCriteria(TCustomer);
MyCriteria.AutoDestroy := false;
// You MUST destroy MyCriteria eventually, even after retrieving results
7.2
7.3
Fluent Interface
The criteria objects you create implement a fluent interface. This means that most methods in the class will return an instance of the object itself. This is just a easier way to build your queries.
So instead of building the query like this:
var
Results: TObjectList<TCustomer>;
Criteria: TCriteria<TCustomer>;
Filter: TCustomCriterion;
begin
Criteria := Manager1.Find<TCustomer>;
Filter := Linq[ 'Name' ] = 'Mia Rosenbaum' ;
Criteria.Add(Filter);
Results := Criteria.List;
You can simply write it this way:
var
Results: TObjectList<TCustomer>;
begin
Results := Manager1.Find<TCustomer>
.Add(Linq[ 'Name' ] = 'Mia Rosenbaum' )
.List;
Almost all the examples in this chapter uses the fluent interface so you can fully understand how to use it.
Retrieving Results
Usually query results are a list of objects of an specified class. You usually call
List or List<T> methods to
retrieve an object list , or Open to get a
fetch-ondemand cursor . If you use a list, this will retrieve you a TList<T> object with all
the queries objects. If you are sure your query will return a single value, use
UniqueResult (or UniqueValue for projections), which will return a single instance of the object.
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It's also important to know how
memory management is performed with the
queried objects, so you properly know when you need to destroy the retrieved results, and when you don't. Also, you don't need to destroy the
query you created using CreateCriteria/Find, it's automatically destroyed when you query
the results.
The following topics describe different ways of retrieving the results of a query:
7.3.1
Retrieving an Object List
After building your query, you can use List method to retrieve filtered/ordered objects. The method to be used depends on how you created your TCriteria object, it could be List or List<T>. The result type will always be a TList<T> where T is the class you are filtering.
If you created the criteria using non-generic Find method, you will need to call
List<T> method.
var
Results: TList<TCustomer>;
MyCriteria: TCriteria;
begin
MyCriteria := ObjectManager1.Find(TCustomer);
// <snip> Build the query
// Retrieve results
Results := MyCriteria.List<TCustomer>;
If you created the generic criteria using Find<T> or CreateCriteria<T> method, just call List method and it will return the correct object list:
var
Results: TList<TCustomer>;
MyCriteria: TCriteria<TCustomer>;
begin
MyCriteria := ObjectManager1.Find<TCustomer>;
// <snip> Build the query
// Retrieve results
Results := MyCriteria.List;
Using this approach, a query will be executed, all objects will be fetched from the database, connection will be closed and a newly created TList<T> object will be returned with all fetched objects. You must later destroy the TList<T> object.
7.3.2
Unique Result
If you are sure your query will return a single value, use UniqueResult instead
(or UniqueResult<T> for non-generic criteria). Instead of a TList<T>, it will just
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return an instance of T object:
var
UniqueCustomer: TCustomer;
MyCriteria: TCriteria<TCustomer>;
begin
MyCriteria := ObjectManager1.Find<TCustomer>;
// <snip> Build the query
// Retrieve the single result
UniqueCustomer := MyCriteria.UniqueResult;
If the query returns no objects, then UniqueResult will return nil. If the query returns more than one different object, an exception will be raised.
Note that if the query returns more than one record, but all records relate to the same object, then no exception will be raised, and the unique object will be returned.
7.3.3
Fetching Objects Using Cursor
Alternatively to
, you can get results by using a cursor.
With this approach, Aurelius executes a query in the database and returns a cursor for you to fetch objects on demand. In this case, the query will remain open until you destroy the cursor. While this approach has the advantage to keeping a database connection alive, it takes advantage of fetch-on-demand features of the underlying component set you are using, allowing you to get initial results without having to fetch all the objects returned. You don't even need to fetch all results, you can close the cursor before it. Cursor can also be used in
TAureliusDataset to make it more responsive to visual controls like DB
Grids.
To obtain a cursor, use the Open method:
var
Results: TList<TCustomer>;
MyCriteria: TCriteria<TCustomer>;
Cursor: TCriteriaCursor;
FetchedCustomer: TCustomer;
begin
MyCriteria := ObjectManager1.Find<TCustomer>;
// <snip> Build the query
// Retrieve results
Cursor := MyCriteria.Open;
try while
Cursor.Next
do begin
FetchedCustomer := Cursor.Get<TCustomer>;
// Do something with FetchedCustomer
end
;
finally
Cursor.Free;
end
;
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The Open method returns a TCriteriaCursor object which must be later destroyed. The underlying TCriteria object (MyCriteria variable in the example above) is automatically destroyed when cursor is destroyed.
The TCriteriaCursor object is declared as following:
TCriteriaCursor =
class abstract
(TInterfacedObject,
ICriteriaCursor)
public function
Next: boolean;
virtual
;
abstract
;
function
Fetch: TObject;
virtual
;
abstract
;
function
BaseClass: TClass;
virtual
;
abstract
;
function
Get<T:
class
>: T;
end
;
Next method increases cursor position. If result is true, then the new position is valid and there is an object to fetch. If result is false, there are no more objects to be fetched, and cursor must be destroyed. It's important to note that when the cursor is open, it remains in an undefined position. You must call Next method first, before fetching any object. If the very Next call returns false, it means the cursor has no records.
Fetch method is used to retrieve the object in the current cursor position. If
Next was never called, or if the result of last Next call was false, Fetch will return unpredictable values. Never call Fetch in such situation.
Get<T> method is just a strong-typed version of Fetch method.
BaseClass method returns the base class used in the criteria query. In the example above, base class would be TCustomer.
As you might have noticed in the TCriteriaCursor declaration above, it implements an ICriteriaCursor interface. That interface is defined as following:
ICriteriaCursor =
interface function
Next: boolean;
function
Fetch: TObject;
function
BaseClass: TClass;
end
;
You can use such interface instead of using TCriteriaCursor, so you don't need to worry about destroying the cursor object - Delphi reference counting will take care of it. The only difference is that ICriteriaCursor doesn't declare the
Get<T> method, so you would have to use Fetch method. The code below illustrates how to use ICriteriaCursor:
var
Results: TList<TCustomer>;
MyCriteria: TCriteria<TCustomer>;
Cursor: ICriteriaCursor;
FetchedCustomer: TCustomer;
begin
MyCriteria := ObjectManager1.Find<TCustomer>;
// <snip> Build the query
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// Retrieve results
Cursor := MyCriteria.Open;
while
Cursor.Next
do begin
FetchedCustomer := TCustomer(Cursor.Fetch);
// Do something with FetchedCustomer
end
;
// No need to destroy cursor
7.3.4
Results with Projections
If you added
to your query, the results will not be entity objects anymore, but instead an special object type that holds a list of values. For example, if you use sum and grouping in your orders, you will not receive a list of TOrder objects anymore, but instead a list of values for the sum results and grouping name.
If that's the case, you should use either:
- ListValues method (if you want to
retrieve an object list . This is the
equivalent of List method for entity objects).
- UniqueValue method (if you want to
retrieve an unique value . This is the
equivalent of UniqueResult method for entity objects).
- Open method to
retrieve results using a cursor
. In this case, the method is the same for either projected or non-projected queries. The only different is the type of object that will be returned.
When using queries with projections, the object returned is a TCriteriaResult object. The TCriteriaResult is an object that has a default property Values which you can use to retrieve the values using an index:
var
Results: TObjectList<TCriteriaResult>;
MyCriteria: TCriteria<TCustomer>;
FirstValueInFirstRecord: Variant;
begin
MyCriteria := ObjectManager1.Find<TCustomer>;
// <snip> Build the query and add projections to it
// Retrieve projected results
Results := MyCriteria.ListValues;
FirstValueInFirstRecord := Results[ 0 ].Values[ 0 ];
Alternatively, you can find the value by name. The name is specified by the alias of projections. If no alias is specified, an internal autonumerated name is used.
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7.4
uses
{...}
, Aurelius.Criteria.Projections;
var
Results: TObjectList<TCriteriaResult>;
begin
Results := Manager.Find<TTC_Estimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ).As_( 'EstimateSum' ))
.Add(TProjections.Group( 'c.Name' ))
)
.Add(Linq[ 'c.Name' ].Like( 'M%' ))
.OrderBy( 'EstimateSum' )
.ListValues;
EstimateSum := Results[ 0 ].Values[ 'EstimateSum' ];
CustomerName := Results[ 0 ].Values[ 1 ];
// no alias specified for c.Name
end
;
If the property doesn't exist, an error is raised. TCriteriaResult also has an additional HasProp method for you to check if the specified value exists. The following code contains the TCriteriaResult public methods and properties.
TCriteriaResult =
class public function
HasProp(PropName:
string
): boolean;
function
HasProp(PropName:
string
): boolean;
property
PropNames[
Index
: integer]:
string read
GetPropName;
property
Values[
Index
: integer]: Variant
read
GetValue;
default
;
property
Values[PropName:
string
]: Variant
read
GetPropValue;
default
;
property
Count: integer
read
GetCount;
end
;
It's important to note that TCriteriaResult objects are not managed by the
TObjectManager, so the retrieved objects must be destroyed. When using
ListValues method to retrieve the results, the returned list is a TObjectList<T> object that already has its OwnsObjects property set to true. So destroyed the list should be enough. When using UniqueValue or Open methods, you must be sure to destroy the TCriteriaResult objects.
Filtering Results
You can narrow the result of your query by adding filter expressions to your query. This is similar to the WHERE clause in an SQL statement. Any expression object descends from TCustomCriterion, and you can use Add or Where methods to add such objects to the query:
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{...}
, Aurelius.Criteria.Linq;
Results := Manager1.Find<TCustomer>
.Where(Linq[ 'Name' ] = 'Mia Rosenbaum' )
.List;
You can add more than one expression to the query. The expression will be combined with an "and" operator, which means only objects which satisfies all conditions will be returned (Add and Where methods are equivalents):
Results := Manager1.Find<TCustomer>
.Add(Linq[ 'Country' ] = 'US' )
.Add(Linq[ 'Age' ] = 30 )
.List; or you can simply use logical operators directly:
Results := Manager1.Find<TCustomer>
.Where((Linq[ 'Country' ] = 'US' )
and
(Linq[ 'Age' ] = 30 ))
.List;
In the topics below you will find all the advanced features for building queries in
Aurelius:
Creating Expressions Using Linq
7.4.1
Creating Expressions Using TLinq
To filter results you must add TCustomCriterion objects to the query object.
The TCustomCriterion objects just represent a conditional expression that the object must satisfy to be included in the result. To create such objects, you can use the Linq factory. It's declared in Aurelius.Criteria.Linq unit:
uses
Aurelius.Criteria.Linq
Linq variable is just a helper object with several methods (Equal, GreaterThan, etc.) that you can use to easily create TCustomCriterion instances. For example, the following lines produce the same object and will result in the same query:
Criterion :=
TSimpleExpression.Create(TPropertyProjection.Create( 'Age' ), 30 , eoGreater));
Criterion := Linq.GreaterThan( 'Age' , 30 );
Criterion := Linq[ 'Age' ] > 30 ;
You can always use the default indexed property passing the property name to start using queries. That will represent a property projection:
Linq[<propertyname>]
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Note that in all the methods listed here, the method can receive a string
(representing a property name) or a
for more details.
You can use Linq to create the following conditions:
7.4.1.1
Equals
Retrieves a condition where the specified property (or projection) value must be equals to the specified value or projection. You can use Equals or Eq method, or the = operator, they all do the same.
Example - Return customers where Name property is equal to "Mia Rosenbaum".
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ] = 'Mia Rosenbaum' )
.List;
Another way to write it:
Results := Manager.Find<TCustomer>
.Where(Linq.Eq( 'Name' , 'Mia Rosenbaum' ))
.List;
7.4.1.2
Greater Than
Retrieves a condition where the specified property (or projection) value must be greater than the specified value. You can use either GreatherThan or Gt method, or the > operator, they all do the same.
Example - Return customers where Birthday property is greater than 10-10-
1981 and less than 02-02-1986.
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Results := Manager.Find<TCustomer>
.Where(
(Linq[ 'Birthday' ] > EncodeDate( 1981 , 10 , 10 ))
and
(Linq[ 'Birthday' ] < EncodeDate( 1986 , 2 , 2 ))
)
.List; another way to write it:
Results := Manager.Find<TCustomer>
.Add(Linq.GreaterThan( 'Birthday' , EncodeDate( 1981 , 10 , 10 )))
.Add(Linq.LessThan( 'Birthday' , EncodeDate( 1986 , 2 , 2 )))
.List;
7.4.1.3
Greater Than or Equals To
Retrieves a condition where the specified property (or projection) value must be greater than or equals to the specified value. You can use either
GreaterOrEqual or Ge method, or >= operator, they all do the same.
Example - Return customers where Birthday property is greater than or equals to 10-10-1981 and less than or equals to 02-02-1986.
Results := Manager.Find<TCustomer>
.Where(
(Linq[ 'Birthday' ] >= EncodeDate( 1981 , 10 , 10 ))
and
(Linq[ 'Birthday' ] <= EncodeDate( 1986 , 2 , 2 ))
)
.List; another way to write it:
Results := Manager.Find<TCustomer>
.Add(Linq.GreaterOrEqual( 'Birthday' , EncodeDate( 1981 , 10 ,
10 )))
.Add(Linq.LessOrEqual( 'Birthday' , EncodeDate( 1986 , 2 , 2 )))
.List;
7.4.1.4
Less Than
Retrieves a condition where the specified property (or projection) value must be less than the specified value. You can use either LessThan or Lt method, or
< operator, they all do the same.
Example - Return customers where Birthday property is greater than 10-10-
1981 and less than 02-02-1986.
Results := Manager.Find<TCustomer>
.Where(
(Linq[ 'Birthday' ] > EncodeDate( 1981 , 10 , 10 ))
and
(Linq[ 'Birthday' ] < EncodeDate( 1986 , 2 , 2 ))
)
.List;
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another way to write it:
Results := Manager.Find<TCustomer>
.Add(Linq.GreaterThan( 'Birthday' , EncodeDate( 1981 , 10 , 10 )))
.Add(Linq.LessThan( 'Birthday' , EncodeDate( 1986 , 2 , 2 )))
.List;
7.4.1.5
Less Than Or Equals To
Retrieves a condition where the specified property (or projection) value must be less than or equals to the specified value. You can use either LessOrEqual or Le method, or <= they both do the same.
Example - Return customers where Birthday property is greater than or equals to 10-10-1981 and less than or equals to 02-02-1986.
Results := Manager.Find<TCustomer>
.Where(
(Linq[ 'Birthday' ] >= EncodeDate( 1981 , 10 , 10 ))
and
(Linq[ 'Birthday' ] <= EncodeDate( 1986 , 2 , 2 ))
)
.List; another way to write it:
Results := Manager.Find<TCustomer>
.Add(Linq.GreaterOrEqual( 'Birthday' , EncodeDate( 1981 , 10 ,
10 )))
.Add(Linq.LessOrEqual( 'Birthday' , EncodeDate( 1986 , 2 , 2 )))
.List;
7.4.1.6
Like
Retrieves a condition where the specified property (or projection) value contains the text specified. It's equivalente to the LIKE operator in SQL statements. You must specify the wildchar % in the value condition.
Example - Return customers where Sex property is not null, and Name starts with "M".
Results := Manager.Find<TCustomer>
.Where(
Linq[ 'Sex' ].IsNotNull
and
Linq[ 'Name' ].Like( 'M%' )
)
.List; another write to write it:
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Results := Manager.Find<TCustomer>
.Where(
Linq.IsNotNull( 'Sex' )
and
Linq.Like( 'Name' , 'M%' )
)
.List;
7.4.1.7
IsNull
Retrieves a condition where the specified property (or projection) contains a null value.
Example - Return customers where Sex property is female, or Sex property is null.
Results := Manager.Find<TCustomer>
.Where(
(Linq[ 'Sex' ] = tsFemale)
or
Linq[ 'Sex' ].IsNull
)
.List;
Another way to write it:
Results := Manager.Find<TCustomer>
.Where(
Linq.Eq( 'Sex' , tsFemale)
or
Linq.IsNull( 'Sex' )
)
.List;
7.4.1.8
IsNotNull
Retrieves a condition where the specified property (or projection) does not contain a null value.
Example - Return customers where Sex property is not null, and Name starts with "M".
Results := Manager.Find<TCustomer>
.Where(
Linq[ 'Name' ].Like( 'M%' )
and
Linq[ 'Sex' ].IsNotNull
)
.List;
Another way to write it:
Results := Manager.Find<TCustomer>
.Where(
Linq.Like( 'Name' , 'M%' )
and
Linq.IsNotNull( 'Sex' )
)
.List;
7.4.1.9
Identifier Equals
Retrieves a condition where the identifier of the specified class is equal to a value. This is very similar to using Equals, but in this case you don't need to specify the property name - Aurelius already knows that you are referring to
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the Id. Also, for
composite id's , you can provide an array of variant for all the
values of the composite id, the query will compare all table columns belonging to the composite id with all values provided in the array of variant.
Example - Return customer where identifier is equal to 1
Customer := Manager.Find<TCustomer>
.Where(Linq.IdEq( 1 ))
.UniqueResult;
Example - Using composite id: return patient where last name is "Smith" and first name is "John" (considering that the id of this class is made of properties
LastName and FirstName:
var
Id: Variant;
Person: TPerson;
begin
Id := VarArrayCreate([ 0 , 1 ], varVariant);
Id[ 0 ] := 'Smith' ;
// last name
Id[ 1 ] := 'John' ;
// first name
Person := Manager.Find<TPerson>
.Where(Linq.IdEq(Id))
.UniqueResult;
7.4.1.10 Sql Expression
Creates a custom SQL expression condition. Use this for total flexibility, if you might fall into a situation where regular query filters provided by Aurelius are not enough. The SQL you provide in this expression must conform with the underlying database syntax. Aurelius doesn't perform any syntax conversion
(except aliases and parameters, see below).
Example - Return customer where database column NAME is equal to "Mia
Rosenbaum"
Results := Manager.Find<TCustomer>
.Where(Linq.Sql( 'A.CUSTOMER_NAME = ''Mia Rosenbaum''' ))
.List;
Aliases
Note that since the SQL expression will be just injected in the SQL statement, you must be sure it will work. In the example above, the exact alias name ("A") and field name ("CUSTOMER_NAME") needed to be included.
In order to prevent you from knowing which alias to use (which is especially tricky when Aurelius need to use joins in SQL statement), you can use placeholders (aliases) between curly brackets. Write the name of the property inside curly brackets and Aurelius will translate it into the proper alias.fieldname
format according to eh SQL. The following example does the same as the previous one, but instead of using the field name directly, you use the name of property TCustomer.Name.
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Results := Manager.Find<TCustomer>
.Where(Linq.Sql( '{Name} = ''Mia Rosenbaum''' ))
.List;
When querying associations, you can also prefix the property name with the alias of the association (see how to query
Results := Manager.Find<TCustomer>
.CreateAlias( 'Country' , 'c' )
.Where(Linq.Sql( '{c.Name} = ''United States''' ))
.List;
Note that when you use subcriteria, the context of the property in curly brackets will be the subcriteria class. The following query is equivalent to the previous one:
Results := Manager.Find<TCustomer>
.SubCriteria( 'Country' )
.Where(Linq.Sql( '{Name} = ''United States''' ))
.List<TTC_Customer>;
Parameters
You can also use parameters in the Sql projection, to avoid having to use specific database syntax for literals. For example, if you want to compare a field with a date value, you would need to specify a date literal with a syntax that is compatible with the database SQL syntax. To avoid this, Aurelius allows you to use parameters in Sql expression. You can use up to two parameters in each expression. The parameters must be indicated by a question mark ("?") and the type of parameters must be provided in a generic parameter for the Sql method:
Example - using one parameter of type TSex
Results := Manager.Find<TCustomer>
.Where(Linq.Sql<TSex>( '{Sex} IN (?)' , TSex.tsFemale))
.List;
Example - using two parameters of type TDate
Results := Manager.Find<TEstimate>
.Where(
Linq.Sql<TDate, TDate>(
'{IssueDate} IS NULL OR (({IssueDate} > ?) AND
({IssueDate} < ?))' ,
EncodeDate( 1999 , 2 , 10 ), EncodeDate( 2000 , 8 , 30 ))
)
.List;
7.4.1.11 Starts With
Retrieves a condition where the specified property (or projection) string value must start with the specified value.
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Example - Return customers where Name property starts with "Mia".
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ].StartsWith( 'Mia' ))
.List;
Alternative way to write it:
Results := Manager.Find<TCustomer>
.Where(Linq.StartsWith( 'Name' , 'Mia' ))
.List;
7.4.1.12 Ends With
Retrieves a condition where the specified property (or projection) string value must end with the specified value.
Example - Return customers where Name property ends with "Junior".
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ].EndsWith( 'Junior' ))
.List;
Alternative way to write it:
Results := Manager.Find<TCustomer>
.Where(Linq.EndsWith( 'Name' , 'Junior' ))
.List;
7.4.1.13 Contains
Retrieves a condition where the specified property (or projection) string value must contain the specified value.
Example - Return customers where Name property contains "Walker".
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ].Contains( 'Walker' ))
.List;
Alternative way to write it:
Results := Manager.Find<TCustomer>
.Where(Linq.Contains( 'Name' , 'Walker' ))
.List;
7.4.1.14 In
The actual method name is "_In". Checks if the value of a specified property
(or projection) belongs to a set of predefined values. The predefined set of values can be of type string, integer or enumerated.
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Example - Return invoices where Status property is either Approved or
Rejected, and year of issue date is 2016 or 2014.
Results := Manager.Find<TInvoice>
.Add(Linq[ 'Status' ]._In([TInvoiceStatus.Approved,
TInvoiceStatus.Rejected))
.Add(Linq[ 'IssueDate' ].Year._In([ 2016 , 2014 ])
.List;
Alternative way to write it:
Results := Manager.Find<TInvoice>
.Add(Linq._In( 'Status' , [TInvoiceStatus.Approved,
TInvoiceStatus.Rejected))
.Add(Linq._In( 'IssueDate' , [ 2016 , 2014 ]);
.List;
7.4.1.15 Comparing Projections
In most of the examples of filtering in queries, we used just the name of the property and compare it to a value. For example:
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ] = 'Mia' )
.List;
But Aurelius query is much powerful than that. Linq['Name'] actually represents a
projection , and you can use any projection in any expression you want.
This gives you great flexibility since you can
Example - Return Orders where cancelation date is greater than shipping date:
Results := Manager.Find<TOrder>
.Where(Linq[ 'CancelationDate' ] > Linq[ 'ShippingDate' ])
.List; or you can even use complex expressions. We can for example change the above query to bring all orders where the year of cancelation date is the same as the year of shipping date:
Results := Manager.Find<TOrder>
.Where(Linq[ 'CancelationDate' ].Year =
Linq[ 'ShippingDate' ].Year)
.List;
7.4.2
Associations
You can add condition expressions to associations of the class being queried.
For example, you can retrieve invoices filtered by the name of invoice
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customer.
To add a condition for an association, you have two options: use subcriteria or aliases.
Using aliases
You can create an alias for an association to filter by sub properties of such association.
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Where(Linq[ 'c.Name' ].Like( 'M%' ))
.List;
Calling CreateAlias does not return a new TCriteria instance, but instead it returns the original TCriteria. So the expression context is still the original class
(in the example above, TEstimate). Thus, to reference a Customer property the
"c" alias prefix was needed. Note that since the original TCriteria<TEstimate> object is being used, you can call List method (instead of TList<T>).
Just like SubCriteria calls, you can also use nested CreateAlias methods, by settings aliases for associations of associations. It's important to note that the context in the fluent interface is always the original TCriteria class:
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'ct' )
.CreateAlias( 'ct.Country' , 'cn' )
.Where(Linq[ 'cn.Name' ] = 'United States' )
.List;
Using SubCriteria
You can alternatively create a sub-criteria which related to the association being filtered, using SubCriteria method of the TCriteria object itself. It returns a new TCriteria object which context is the association class, not the main class being queried.
Results := Manager.Find<TInvoice>
.SubCriteria( 'Customer' )
.Where(Linq[ 'Name' ].Like( 'M%' ))
.List<TInvoice>;
In the example above the class TInvoice has a property Customer which is an association to the TCustomer class. The filter "Name = 'M%'" is applied to the customer, not the invoice. SubCriteria method is being called and receives
"Customer" parameter, which is the name of associated property. This returns a new TCriteria object. The expressions added to it related to TCustomer class, that's why 'Name' refers to the TCustomer.Name property, not TInvoice.Name
(if that ever existed).
Note that SubCriteria method returns a TCriteria method (the non-generic version). That's why we need to call List<TInvoice> method (not just List).
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You can have nested SubCriteria calls, there is not a level limit for it. In the example below, the query returns all estimates for which the country of the customer is "United States".
Results := Manager.Find<TEstimate>
.SubCriteria( 'Customer' )
.SubCriteria( 'Country' )
.Where(Linq[ 'Name' ] = 'United States' )
.List<TEstimate>;
7.5
Mixing SubCriteria and aliases
You can safely mix SubCriteria and CreateAlias calls in the same query:
Results := Manager.Find<TEstimate>
.SubCriteria( 'Customer' )
.CreateAlias( 'Country' , 'cn' )
.Where(Linq[ 'cn.Name' ] = 'United States' )
.List<TEstimate>;
Specifying Eager fetching for associations loaded as lazy by default
Your class mapping might have defined associations to be marked as
lazyloaded (using proxies). This means if you retrieve one hundred records and you
want to access the associated object, one hundred SQL statements will be executed to retrieve such value. You can optionally override the default loading mechanism and set the association to be eager-loaded. This way Aurelius will build an extra JOIN in the SQL statement to retrieve the associated objects in a single SQL. You do this by passing TFetchMode.Eager as the third parameter of CreateAlias or second parameter of SubCriteria:
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'ct' , TFetchMode.Eager)
.List; with the query above, even if TEstimate.Customer association is set as lazyloading, Aurelius will create a single SQL with a JOIN between estimates and customers and retrieve all customers at once. This gives you an extra degree of flexibility when it comes to optimize your application.
Ordering Results
You can order the results by any property of the class being query, or by a property of an association of the class. Just use either AddOrder or OrderBy methods of the TCriteria object. You must define name of the property (or projection) being ordered, and if the order is ascending or descending. See examples below:
Retrieve customers ordered by Name
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Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ].Like( 'M%' ))
.OrderBy( 'Name' )
.List;
Same query using AddOrder (instead of OrderBy):
Results := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ].Like( 'M%' ))
.AddOrder(TOrder.Asc( 'Name' ))
.List;
You can also use
association aliases in orderings.
Retrieve all estimates which IssueDate is not null, ordered by customer name in descending order (second parameter in OrderBy specify ascending/descending false means descending, it's true by default):
7.6
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Where(Linq[ 'IssueDate' ].IsNotNull)
.OrderBy( 'c.Name', false )
.List;
Same query using AddOrder:
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Add(Linq[ 'IssueDate' ].IsNotNull)
.AddOrder(TOrder.Desc( 'c.Name' ))
.List;
If you need to order by complex expressions, it's recommended that you use a
Alias projection for it. In the example below, the order refers to the
EstimateSum alias, which is just an alias for the sum expression
Results := Manager.Find<TTC_Estimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ).As_( 'EstimateSum' ))
.Add(TProjections.Group( 'c.Name' ))
)
.Where(Linq[ 'c.Name' ].Like( 'M%' ))
.AddOrder(TOrder.Asc( 'EstimateSum' ))
.ListValues;
Projections
You can make even more advanced queries in Aurelius by using projections. For example, instead of selecting pure object instances (TCustomer for example) you can perform grouping, select sum, average, a function that retrieves the year of a date, among others. There is a formal definition for projection, but
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you can think of a projection just as an expression that returns a value, for example, a call to Sum function, a literal, or the value of a property.
Usually you will use projections to return specific/calculated values instead of objects, or to perform complex condition expressions (to retrieve all customers where the year of birthday column is equal to 1999).
For example, the following query retrieves the number of invoices for the year
2013 and illustrates how to use projections in both select and where parts of the query.
uses
{...}
, Aurelius.Criteria.Linq,
Aurelius.Criteria.Projections;
TotalInvoicesFor2013 := Manager.Find<TInvoice>
.Select(TProjections.Count( 'Id' ))
.Where(Linq[ 'IssueDate' ].Year = 2013 )
.UniqueValue;
The following topics explain in details what projections are and how you can use them.
Creating Projections Using TProjections
7.6.1
Projections Overview
Any projection object descends from TProjection class. To make a query return projections (calculated values) instead of entities, use the SetProjections or
Select method.
The example below calculates the sum of all estimates where the customer name beings with "M".
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{...}
, Aurelius.Criteria.Linq,
Aurelius.Criteria.Projections;
Value := Manager.Find<TEstimate>
.Select(TProjections.Sum( 'EstimateNo' ))
.CreateAlias( 'Customer' , 'c' )
.Where(Linq[ 'c.Name' ].Like( 'M%' ))
.UniqueValue;
You can only have a single projection specified for the select part of the query.
If you call SetProjections or Select method twice in a single query, it will replace the projection specified in the previous call. If you want to specify multiple projections, using a projection list:
Query over estimates, retrieving the sum of EstimateNo, grouped by customer name.
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ))
.Add(TProjections.Group( 'c.Name' ))
)
.ListValues;
Note that when using projections, the query does not return instances of the queried class (TEstimate in example above). Instead, it returns a list of
TCriteriaResult objects, which you can use to retrieve the projection values.
See more in
The Select method is exactly the same as the method SetProjections, it's just included as an option so it looks better in some queries.
In all the examples above, the TProjection objects added to the criteria were created using the TProjections factory class. The TProjections is just a helper class with several class methods that you can use to easily create TProjection instances.
You can also use projections in the where clause to add complex queries. Many of the
you can use in a query can compare projections, for example:
YoungCustomers := Manager.Find<TCustomer>
.Where(Linq[ 'Birthday' ].Year > 2000 )
.List; will list all customers which year of birth is greather than 2000.
7.6.2
Creating Projections Using TProjections
Any projection you want to use is a TProjection object. To create such objects, you can use the TProjections factory class. It's declared in
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Aurelius.Criteria.Projections unit.
uses
Aurelius.Criteria.Projections
The TProjections class is just a helper class with several class methods (Sum,
Group, etc.) that you can use to easily create TProjection instances. For example, the following lines produce the same object:
Projection := TAggregateProjection.Create( 'sum' ,
TPropertyProjection.Create( 'Total' ));
Projection := TProjections.Sum( 'Total' );
You can use TProjections to create the following projections:
7.6.2.1
Aggregated Functions
There are several methods in TProjections class that create a projection that represents an aggregated function over a property value (or a projection).
Available methods are:
Sum: Calculated the sum of values
Min: Retrieves the minimum value
Max: Retrieves the maximum value
Avg: Calculates the average of all values
Count: Retrieves the number of objects the satisfy the condition
Calculates the sum of all estimates where the customer name beings with "M".
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Value := Manager.Find<TEstimate>
.Select(Linq[ 'EstimateNo' ].Sum)
.CreateAlias( 'Customer' , 'c' )
.Where(Linq[ 'c.Name' ].Like( 'M%' ))
.UniqueValue;
Alternative way to write the same query:
Value := Manager.Find<TEstimate>
.Select(TProjections.Sum( 'EstimateNo' ))
.CreateAlias( 'Customer' , 'c' )
.Where(Linq[ 'c.Name' ].Like( 'M%' ))
.UniqueValue;
7.6.2.2
Prop
Creates a projection that represents the value of a property. In most cases, you will use that projection transparently, because the following constructions will return such projection for you:
Linq[ 'Name' ]
Linq[ 'IssueDate' ]
Alternatively there are overloads for almost all methods in Linq and TProjection classes that accept a string instead of a projection. The string represents a property name and internally all it does is to create a property projection using
Prop method.
The example below illustrates how Prop method can be used.
The following two queries are equivalent, both retrieve the name of the customers ordered by the Name:
Results := Manager.Find<TCustomer>
.Select(Linq[ 'Name' ])
.AddOrder(TOrder.Asc(Linq[ 'Name' ]))
.ListValues;
{...}
Results := Manager.Find<TCustomer>
.Select(TProjections.Prop( 'Name' ))
.AddOrder(TOrder.Asc(TProjections.Prop( 'Name' )))
.ListValues;
The following three queries are also equivalent:
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Results := Manager.Find<TCustomer>
.Add(Linq.Eq( 'Name' , 'Mia Rosenbaum' ))
.List;
{...}
Results := Manager.Find<TCustomer>
.Add(Linq.Eq(TProjections.Prop( 'Name' ), 'Mia Rosenbaum' ))
.List;
{...}
Results := Manager.Find<TCustomer>
.Add(Linq.Eq(Linq[ 'Name' ], 'Mia Rosenbaum' ))
.List;
7.6.2.3
Group
Creates a projection that represents a group. This is similar to the GROUP BY clause in an SQL statement, but the difference is that you don't need to set a
Group By anywhere - you just add a grouped projection to the projection list and Aurelius groups is automatically.
The query below retrieves the sum of EstimateNo grouped by customer name.
The projected values are the EstimateNo sum, and the customer name. Since the customer name is already one of the selected projections and it's grouped, that's all you need - you don't have to add the customer name in some sort of
Group By section.
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ))
.Add(TProjections.Group( 'c.Name' ))
)
.ListValues;
7.6.2.4
Add
Adds two numeric values.
Example:
Results := Manager.Find<TInvoice>
.Select(Linq[ 'Total' ] + Linq[ 'Additional' ])
.List;
Another way to write it:
Results := Manager.Find<TInvoice>
.Select(Linq.Add(Linq[ 'Total' ], Linq[ 'Additional' ]))
.List;
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7.6.2.5
Subtract
Subtracts two numeric values.
Example:
Results := Manager.Find<TInvoice>
.Select(Linq[ 'Total' ] - Linq[ 'Discount' ])
.List;
Another way to write it:
Results := Manager.Find<TInvoice>
.Select(Linq.Subtract(Linq[ 'Total' ], Linq[ 'Discount' ]))
.List;
7.6.2.6
Multiply
Multiplies two numeric values.
Example:
Results := Manager.Find<TInvoiceItem>
.Select((Linq[ 'Quantity' ] *
Linq[ 'UnitaryValue' ]).As_( 'TotalValue' ))
.List;
Another way to write it:
Results := Manager.Find<TInvoiceItem>
.Select(Linq.Multiply(Linq[ 'Quantity' ],
Linq[ 'UnitaryValue' ]).As_( 'TotalValue' ))
.List;
7.6.2.7
Divide
Divides two numeric values.
Example:
Results := Manager.Find<TInvoiceItem>
.Select((Linq[ 'Total' ] / Linq[ 'Quantity' ]).As_( 'ItemValue' ))
.List;
Another way to write it:
Results := Manager.Find<TInvoiceItem>
.Select(Linq.Multiply(Linq[ 'Total' ],
Linq[ 'Quantity' ]).As_( 'ItemValue' ))
.List;
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Aurelius ensures consistency among different databases. When performing division between two integer values, many databases truncate the result and return an integer, rounded value. For example, 7 / 5 results 1. Some databases do not behave that way.
In Aurelius, the division operator performs with Pascal behavior: the result is a floating point operation, even when dividing two integer values. Thus, 7 / 5 will return 1.4, as expected.
7.6.2.8
Condition
Creates a conditional projection. It works as an If..Then..Else clause, and it's equivalente to the "CASE..WHEN..ELSE" expression in SQL.
Retrieves the customer name and a string value representing the customer sex.
If sex is tsFemale, return "Female", if it's tsMale return "Male". If it's null, then return "Null".
Results := Manager.Find<TCustomer>
.Select(TProjections.ProjectionList
.Add(Linq[ 'Name' ])
.Add(TProjections.Condition(
Linq[ 'Sex' ].IsNull,
Linq.Literal<
string
>( 'Null' ),
TProjections.Condition(
Linq[ 'Sex' ] = tsMale,
Linq.Literal<
string
>( 'Male' ),
Linq.Literal<
string
>( 'Female' )
)
)
)
)
.ListValues;
7.6.2.9
Literal<T>
Creates a constant projection. It's just a literal value of scalar type T. Aurelius automatically translates the literal into the database syntax. The Literal<T> method is different from Value<T> in the sense that literals are declared directly in the SQL statement, while values are declared as parameters and the value is set in the parameter value.
Retrieves some literal values
Results := Manager.Find<TCustomer>
.Select(TProjections.ProjectionList
.Add(Linq.Literal<
string
>( 'Test' ))
.Add(Linq.Literal<Currency>( 1.53
))
.Add(Linq.Literal<double>( 3.14e-2 ))
.Add(Linq.Literal<integer>( 100 ))
.Add(Linq.Literal<TDateTime>(Date1))
)
.ListValues;
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Another example using Condition projection:
Results := Manager.Find<TCustomer>
.Select(TProjections.ProjectionList
.Add(Linq[ 'Name' ])
.Add(TProjections.Condition(
Linq[ 'Sex' ].IsNull,
Linq.Literal<
string
>( 'Null' ),
TProjections.Condition(
Linq[ 'Sex'] = tsMale,
Linq.Literal<
string
>( 'Male' ),
Linq.Literal<
string
>( 'Female' )
)
)
)
)
.ListValues;
7.6.2.10 Value<T>
Creates a constant projection. It's just a value of scalar type T. It works similar to
Literal<T> method, the difference is that literals are declared directly
in the SQL statement, while values are declared as parameters and the value is set in the parameter value.
7.6.2.11 ProjectionList
Retrieves a list of projections. It's used when setting the projection of a query using Select or SetProjections method. Since only one projection is allowed per query, you define more than one projections by adding a projection list. This method returns a TProjectionList object which defines the Add method that you use to add projections to the list.
Creates a projection list with two proejctions: Sum of EstimateNo and
Customer Name.
Results := Manager.Find<TEstimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Sum( 'EstimateNo' ))
.Add(TProjections.Group( 'c.Name' ))
)
.ListValues;
7.6.2.12 Alias
Associates an alias to a projection so it can be referenced in other parts of criteria. Currently only
can refer to aliased projections. It's useful when you need to use complex expressions in the order by clause - some databases do not accept such expressions, so you can just reference an existing projection in the query, as illustrated below.
Retrieve all estimates grouped by customer name, ordered by the sum of estimates for each customer.
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Results := Manager.Find<TTC_Estimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(Linq[ 'EstimateNo' ].Sum.As_( 'EstimateSum' ))
.Add(Linq[ 'c.Name' ].Group)
)
.Add(Linq[ 'c.Name' ].Like( 'M%' ))
.AddOrder(TOrder.Asc( 'EstimateSum' ))
.ListValues;
Alternatively you can create aliased projections using the TProjections.Alias
method of any simple projection. This query does the same as the previous query:
Results := Manager.Find<TTC_Estimate>
.CreateAlias( 'Customer' , 'c' )
.Select(TProjections.ProjectionList
.Add(TProjections.Alias(TProjections.Sum( 'EstimateNo' ),
'EstimateSum' ))
.Add(TProjections.Group( 'c.Name' ))
)
.Add(Linq.Like( 'c.Name' , 'M%' ))
.AddOrder(TOrder.Asc( 'EstimateSum' ))
.ListValues;
7.6.2.13 Sql Projection
Creates a projection using a custom SQL expression. Use this for total flexibility, if you might fall into a situation where regular projections provided by
Aurelius are not enough. The SQL you provide in this expression must conform with the underlying database syntax. Aurelius doesn't perform any syntax conversion (except aliases, see below).
Example - Return specific projections
Results := Manager.Find<TCustomer>
.CreateAlias( 'Country' , 'c' )
.Select(TProjections.ProjectionList
.Add(Linq[ 'Id' ].As_( 'Id' ))
.Add(TProjections.Sql<
string
>( 'A.CUSTOMER_NAME' ).As_( 'CustNa me' ))
.Add(TProjections.Sql<double>( '{id} * 2' ).As_( 'DoubleId' ))
.Add(TProjections.Sql<integer>( '{c.id} *
2' ).As_( 'DoubleCountryId' ))
)
.ListValues;
Note that since the SQL expression will be just injected in the SQL statement, you must be sure it will work. In the example above, the exact alias name ("A") and field name ("CUSTOMER_NAME") needed to be included in projection
"CustName".
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In order to prevent you from knowing which alias to use (which is especially tricky when Aurelius need to use joins in SQL statement), you can use placeholders (aliases) between curly brackets. Write the name of the property inside curly brackets and Aurelius will translate it into the proper alias.fieldname
format according to eh SQL. In the previous example, projections "DoubleId" and "DoubleCountryId" use placeholderrs that will be replaced by the proper
"Alias.ColumnName" syntax corresponding to the referenced property. "{id}" refers to property TCustomer.Id, while "{c.Id}" refers to property
TCustomer.Country.Id".
The generic parameter in the Sql method must indicate the type returned by the Sql projection.
7.6.2.14 Year
Retrieves the year of a specified date/time value.
Example:
.Where(Linq[ 'IssueDate' ].Year = 2013 )
Year method creates a projection that extracts the year of a date value.
Equivalent code:
.Where(Linq.Eq(TProjections.Year( 'IssueDate' ), 2013 ))
7.6.2.15 Month
Retrieves the month of a specified date/time value.
Example:
.Where(Linq[ 'IssueDate' ].Month = 11 )
Month method creates a projection that extracts the month of a projection with a date value. Equivalent code:
.Where(Linq.Eq(TProjections.Month( 'IssueDate' ), 11 ))
7.6.2.16 Day
Retrieves the day of a specified date.
Example:
.Where(Linq[ 'IssueDate' ].Day = 3 1 )
Day method creates a projection that extracts the day of a projection with a date value. Equivalent code:
.Where(Linq.Eq(TProjections.Day( 'IssueDate' ), 31 ))
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7.6.2.17 Hour
Retrieves the hour of a specified date/time value.
Example:
.Where(Linq[ 'AppointmentTime' ].Hour = 12)
Hour method creates a projection that extracts the hour of a projection with a date/time value. Equivalent code:
.Where(Linq.Gt(TProjections.Hour( 'AppointmentTime' ), 12 ))
7.6.2.18 Minute
Retrieves the minute of a specified date/time value.
Example:
.Where(Linq[ 'AppointmentTime' ].Minute = 45)
Minute method creates a projection that extracts the number of minutes of a projection with a date/time value. Equivalent code:
.Where(Linq.Gt(TProjections.Minute( 'AppointmentTime' ), 45))
7.6.2.19 Second
Retrieves the second of a specified date/time value.
Example:
.Where(Linq[ 'AppointmentTime' ].Second = 45)
Second method creates a projection that extracts the number of seconds of a projection with a date/time value. Equivalent code:
.Where(Linq.Gt(TProjections.Second( 'AppointmentTime' ), 45))
7.6.2.20 Upper
Converts a string value to upper case.
Example:
.Where(Linq[ 'Name' ].Upper = 'JACK' )
Equivalent code:
.Where(Linq.Eq(TProjections.Upper( 'Name' ), 'JACK' ))
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7.6.2.21 Lower
Converts a string value to lower case.
Example:
.Where(Linq[ 'Name' ].Lower = 'jack' )
Equivalent code:
.Where(Linq.Eq(TProjections.Lower( 'Name' ), 'jack' ))
7.6.2.22 Concat
Concatenates two strings.
Example:
.Select(Linq[ 'FirstName' ].Concat( '
' ).Concat(Linq[ 'LastName' ]))
Equivalent code:
.Select(Linq.Concat(Linq.Concat(Linq[ 'FirstName' ], ' - ' ),
Linq[ 'LastName' ]))
Aurelius does not ensure cross-database consistent when it comes to null handling. Oracle treats null as empty strings, so if your expression is concatenating a null value, result will be null in all databases except Oracle, where it will concatenate the two strings normally (considering null as empty string).
7.6.2.23 Length
Returns the number of characters in a string.
Example:
// Return entities which name has less than 10 characters
.Where(Linq[ 'Name' ].Length < 10 )
Equivalent code:
// Return entities which name has less than 10 characters
.Where(Linq.LessThan(TProjections.Length( 'Name' ), 10 ))
7.6.2.24 ByteLength
Returns the number of bytes in a binary property.
Example:
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// Return entities which Photo has less than 65536 bytes
.Where(Linq[ 'Photo' ].ByteLength < 65536 )
Equivalent code:
// Return entities which Photo has less than 65536 bytes
.Where(Linq.LessThan(TProjections.ByteLength( 'Photo' ), 65536 ))
7.6.2.25 Substring
Returns a substring of the specified string.
Example:
// Return the first 5 characters of the name
.Select(Linq[ 'Name' ].Substring( 1 , 5 ))
First parameter is the start index of substring, 1-based. Thus, 1 represents the first character of the string, 2 the second, etc. Second parameter is the length of substring to be returned.
Equivalent code which passes the projection/property name as the first parameter:
// Return the first 5 characters of the name
.Select(TProjections.Substring( 'Name' , 1 , 5 ))
7.6.2.26 Position
Returns the index value of the first character in a specified substring that occurs in a given string.
Example:
// Return entities only if the position of "@" character
//in the EMailAddress property is higher than 5
.Where(Linq[ 'EmailAddress' ].Position( '@' ) > 5 )
The parameter is the substring to be searched for. The result is the index of the first occurrence of the string, 1-based. In other words, if the substring occurs in the first character, the result is 1. If the substring is not found, result is 0.
Equivalent code which passes the projection/property name as the first parameter:
// Return entities only if the position of "@" character
//in the EMailAddress property is higher than 5
.Where(Linq.GreaterThan(TProjections.Position( '@' ,
'EmailAddress' ), 5 )))
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7.7
Polymorphism
Since Aurelius supports
queries are also polymorphic. It means that if you query over a specified class, you might receive objects of that class, or even descendants of that class.
For example, suppose you have a class hierarchy this way:
TAnimal =
class
TBird =
class
(TAnimal);
TMammal =
class
(TAnimal);
TDog =
class
(TMammal);
TCat =
class
(TMammal); when you perform a query like this:
Results := Manager.Find<TMammal>
.Add(Linq[ 'Name' ].Like( 'T%' ))
.List;
You are asking for all mammals which Name begins with "T". This means all mammals, dogs and cats. So in the resulted object list, you might receive instances of TMammal, TDog or TCat classes. Aurelius does it automatically for you, regardless on the inheritance strategy, i.e. if all classes are being saved in the same table or each class is being saved in a different table. Aurelius will be sure to filter out records representing animals and birds, and retrieve only the mammals (including dogs and cats).
You can safely rely on polymorphism with Aurelius in every query, and also of course, when saving and updating objects.
7.8
Paging Results
Aurelius provides methods the allows you to limit query results at server level.
It's the equivalent of "SELECT TOP" or "SELECT..LIMIT" that some databases use (note this is just an analogy, TMS Aurelius will make sure to build the proper SQL statement for each database according to the supported syntax).
You can limit the number of objects retrieved by using the Take method of
TCriteria object:
Results := Manager.Find<TCustomer>
.OrderBy( 'Name' )
.Take( 50 )
.List;
The previous code will retrieve the first 50 TCustomer objects, ordered by name. Using Take(0) will return an empty result. Using Take(-1) is equivalent to not using Take method at all, meaning all records will be returned. Values below -2 (including) are not allowed and might cause errors.
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You can skip the first N objects retrieved by using Skip method:
Results := Manager.Find<TCustomer>
.OrderBy( 'Name' )
.Skip( 10 )
.List;
The previous will retrieve customers ordered by name, by will omit the first 10 customers from the list. Using Skip(0) is equivalent to not using Skip method at all, since it means skipping no records. Negative values are not allowed and might cause errors.
Although you can use Skip and Take methods without specifying an order, it often doesn't make sense.
Skip and Take methods are often used for paging results, i.e., returning objects belonging to an specific page. The following code exemplifies how to return objects belonging to the page PageIdx, with PageSize objects in each page:
Results := Manager.Find<TCustomer>
.OrderBy( 'Name' )
.Skip(PageIdx * PageSize)
.Take(PageSize)
.List;
7.9
Removing Duplicated Objects
Sometimes a query might result in duplicated objects. The following query is an example of such queries:
Results := Manager.Find<TInvoice>
.CreateAlias( 'Items' , 'i' )
.Add(Linq[ 'i.Price' ] = 20 )
.OrderBy( 'InvoiceNo' )
.List;
The above criteria will look for all invoices which have any item with price equals to 20. Just like in SQL, this query is doing a "join" between the invoice and invoice items. This means that if an invoice has two or more items with price equals to 20, the same TInvoice object will be returned more than once in the result list.
If that's not what you want, and you just list all invoices matching the specified criteria, without duplicates, just use RemoveDuplicatedEntities to your criteria:
Results := Manager.Find<TInvoice>
.CreateAlias( 'Items' , 'i' )
.Add(Linq[ 'i.Price' ] = 20 )
.OrderBy( 'InvoiceNo' )
.RemovingDuplicatedEntities
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.List;
And this will bring distinct invoices. This feature is usually useful when you want to filter objects by a criteria applied to many-valued associations, like in the example above, which might return duplicated results.
Please note that the removal of duplicated objects is done at client level by
Aurelius framework, not at database level, so performance might be not good with queries that result too many records.
7.10
Cloning a Criteria
Aurelius TCriteria object also has a Clone method you can use to clone the criteria. This might useful when you want to reuse the criteria multiple times and maybe slightly change from the base criteria:
MyCriteria := Manager.Find<TCustomer>
.Where(Linq[ 'Name' ] = 'Mia' );
ClonedCriteria := MyCriteria.Clone;
ClonedCriteria.OrderBy( 'Id' );
MyResults := MyCriteria.List<TCustomer>;
ClonedResults := ClonedCriteria.List<TCustomer>;
7.11
Refreshing Results
When performing a query, Aurelius will keep exisiting entities in the cache. For example, if your query returns two TCustomer objects with ID's 10 and 15, if there are already instances of those objects in the manager, they will be kept in the cache with existing properties and will not be updated.
Alternatively, you can use Refreshing method when building the criteria to tell
Aurelius that you want existing objects to be objects with current database values.
The query below will bring all TCustomer objects which year of birthday is
1999. If any of those customers are already in the manager, their properties will still be updated with values retrieved from the database:
MyCriteria := Manager.Find<TCustomer>
.Where(Linq[ 'Birthday' ].Year = 1999 )
.Refreshing
.List;
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Chapter
VIII
Data Binding -
TAureliusDataset
TMS Aurelius Documentation
8 Data Binding - TAureliusDataset
TMS Aurelius allows you to bind your entity objects to data-aware controls by using a TAureliusDataset component. By using this component you can for example display a list of objects in a TDBGrid, or edit an object property directly through a TDBEdit or a TDBComboBox. TAureliusDataset is declared in unit Aurelius.Bind.Dataset:
uses
{...}
, Aurelius.Bind.Dataset;
Basic usage is done by these steps:
1. Set the source of data to be associated with the dataset, using
SetSourceList method, or a single object, using SetSourceObject
2. Optionally, create a TField for each property/association/sub-property you want to display/edit. If you do not, default fields will be used.
3. Optionally, specifiy a TObjectManager using the Manager property. If you do not, you must manually persist objects to database.
TAureliusDaset is a TDataset descendant, thus it's compatible with all dataaware controls provided by VCL, the Firemonkey live bindings framework and any 3rd-party control/tool that works with TDataset descendants. It also provides most of TDataset functionality, like calculated fields, locate, lookup, filtering, master-detail using nested datasets, among others.
The topics below cover all TAureliusDataset features.
·
o
o
o
o
Using Criteria for Offline Fetch-On-Demand
·
·
o
o
o
o
o
Dataset Fields (Many-Valued Associations)
o
Heterogeneous Lists (Inheritance)
·
o
New Objects When Inserting Records
o
o
o
Manual Persistence Using Events
·
·
·
·
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·
8.1
Providing Objects
To use TAureliusDataset, you must provide to it the objects you want to display/edit. The objects will become the source of data in the dataset.
The following topics describe several different methods you can use to provide objects to the dataset:
Using Criteria for Offline Fetch-On-Demand
8.1.1
Providing an Object List
A very straightforward way to provide objects to the dataset is specifying an external object list where the objects will be retrieved from (and added to).
You do that by using SetSourceList method:
var
People: TList<TPerson>;
begin
People := Manager.Find<TPerson>.List;
AureliusDataset1.SetSourceList(People);
You can provide any type of generic list to it. You must be responsible for destroying the list object itself, TAureliusDataset will not manage it.
When you insert/delete records in the dataset, objects will be added/removed to the list.
8.1.2
Providing a Single Object
Instead of providing multiple objects, you can alternatively specify a single object.
It's a straightforward way if you intend to use the dataset to just edit a single object.
You must use SetSourceObject method for that:
Customer := Manager.Find<TCustomer>( 1 );
AureliusDataset1.SetSourceObject(Customer);
Be aware that TAureliusDataset always works with lists. When you call
SetSourceObject, the
internal object list is cleared and the specified object is
added to it. The internal list then is used as the source list of dataset. This means that even if you use SetSourceObject method, objects might be added to or removed from the internal list, if you call methods like Insert, Append or
Delete.
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8.1.3
Using Fetch-On-Demand Cursor
You can provide objects to TAureliusDataset by using a query
This approach is especially useful when returning a large amount of data, since you don't need to load the whole object list first and then
provide the whole list to the dataset. Only needed objects are fetched (for example, the objects
being displayed in a TDBGrid that is linked to the dataset). Additional objects will only be fetched when needed, i.e, when you scroll down a TDBGrid, or call
TDataset.Next method to retrieve the next record.
Note that the advantage of this approach is that it keeps an active connection and an active query to the database until all records are fetched (or dataset is closed).
To use a cursor to provide objects, just call SetSourceCursor method and pass the ICriteriaCursor interface you have obtained when
opening a query using a cursor :
var
Cursor: ICriteriaCursor;
begin
Cursor := Manager.Find<TPerson>.Open;
AureliusDataset1.SetSourceCursor(Cursor);
// Or just this single line version:
AureliusDataset1.SetSourceCursor(Manager.Find<TPerson>.Open);
You don't have to destroy the cursor, since it's an interface and is destroyed by reference counting. When the cursor is not needed anymore, dataset will destroy it.
When you call SetSourceCursor, the
internal object list is cleared. When new
objects are fetched, they are added to the internal list. So, the internal list will increase over time, as you navigate forward in the dataset fetching more records.
8.1.4
Using Criteria for Offline Fetch-On-Demand
Another way to provide objects to TAureliusDataset is providing a TCriteria object to it. Just
create a query and pass the TCriteria object using
SetSourceCriteria method.
var
Criteria: TCriteria;
begin
Criteria := Manager.Find<TPerson>;
AureliusDataset1.SetSourceCriteria(Criteria);
// Or just this single line version:
AureliusDataset1.SetSourceCriteria(Manager.Find<TPerson>);
In the code above, Aurelius will just execute the query specified by the
TCriteria and fill the
internal object list with the retrieved objects. This
approach is actually not very different than
providing an object list to the
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8.2
dataset. The real advantage of it is when you use an overloaded version of
SetSourceCriteria that allows paging.
Office fetch-on-demand using paging
SetSourceCriteria method has an overloaded signature that received an integer parameter specifying a page size:
AureliusDataset1.SetSourceCriteria(Manager.Find<TPerson>, 50 );
It means that the dataset will fetch records on demand, but without needing to keep an active database connection.
When you open a dataset after specifying a page size of 50 as illustrated in the code above, only the first 50 TPerson objects will be fetched from the database, and query will be closed. Internally, TAureliusDataset uses the
paging mechanism provided by Take and Skip methods. If more records are
needed (a TDBGrid is scrolled down, or you call TDataset.Next method multiple times, for example), then the dataset will perform another query in the database to retrieve the next 50 TPerson objects in the query.
So, in summary, it's a fetch-on-demand mode where the records are fetched in batches and a new query is executed every time a new batch is needed. The advantage of this approach is that it doesn't retrieve all objects from the database at once, so it's fast to open and navigate, especially with visual controls. Another advantage (when comparing with
is that it works offline - it doesn't keep an open connection to the database.
One disadvantage is that it requires multiple queries to be executed on the server to retrieve all objects.
You don't have to destroy the TCriteria object. The dataset uses it internally to re-execute the query and retrieve a new set of objects. When all records are fetched or the dataset is closed, the TCriteria object is automatically destroyed.
Internal Object List
TAureliusDataset keeps an internal object list that is sometimes used to hold the objects associated with the dataset records. When you provide an
, the internal list is ignored. However, when you use other methods for providing objects, like
using cursor (SetSourceCursor), paged TCriteria
(SetSourceCriteria), or
(SetSourceObject), then the internal list is used to keep the objects.
When the internal list is used, when new records are inserted or deleted, they are added to and removed from the internal list. When fetch-on-demand modes are used (cursor and criteria), fetched objects are incrementally added to the list. Thus, when you open the dataset you might have 20 objects in the list, when you move the cursor to the end of dataset, you might end up with 100 objects in the list.
So, there might be situations where you need to access such list.
TAureliusDataset provides a property InternalList for that. This property is declared as following:
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InternalList: IReadOnlyObjectList;
The list is accessible through a IReadOnlyObjectList, so you can't modify it
(unless, of course, indirectly by using the TDataset itself). The
IReadOnlyObjectList has the following methods:
IReadOnlyObjectList =
interface function
Count: integer;
function
Item(I: integer): TObject;
function
IndexOf(Obj: TObject): integer;
end
;
Count method returns the current number of objects in the list.
Item method returns the object in the position I of the list (0-based)
IndexOf method returns the position of the object Obj in the list (also 0based)
8.3
Using Fields
In TAureliusDataset, each field represents a property in an object. So, for example, if you have a class declared like this:
TCustomer =
class
// <snip>
public property
Id: Integer
read
FId
write
FId;
property
Name:
string read
FName
write
FName;
property
Birthday: Nullable<TDate>
read
FBirthday
write
FBirthday;
end
; when
providing an object of class TCustomer to the dataset, you will be able
to read or write its properties this way:
CustomerName := AureliusDataset1.FieldByName( 'Name' ).AsString;
if
AureliusDataset1.FieldByName( 'Birthday' ).IsNull
then
AureliusDataset1.FieldByName( 'Birthday' ).AsDateTime :=
EncodeDate( 1980 , 1 , 1 );
As with any TDataset descendant, TAureliusDataset will automatically create
, or you can optionally create TField components manually in the dataset, either at runtime or design-time. Creating persistent fields might be useful when you need to access a field that is not automatically present in the default fields, like a
sub-property field or when working with
The following topics explain fields usage in more details:
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Dataset Fields (Many-Valued Associations)
Heterogeneous Lists (Inheritance)
8.3.1
Default Fields and Base Class
When you open the dataset, default fields are automatically created if no persistent fields are defined. TAureliusDataset will create a field for each property in the "base class", either regular fields, or fields representing
The "base class" mentioned is retrieved automatically by the dataset given the way you provided the objects:
1. If you provide objects by passing a generic list to SetSourceList method,
Aurelius will consider the base class as the generic type in the list. For example, if the list type it TList<TCustomer>, then the base class will be
TCustomer.
2. If you provide an object by using SetSourceObject, the base class will just be the class of object passed to that method.
3. You can alternatively manually specify the base class, by using the
ObjectClass property. Note that this must be done after calling SetSourceList or SetSourceObject, because these two methods update the ObjectClass property internally. Example:
AureliusDataset1.SetSourceList(SongList);
AureliusDataset1.ObjectClass := TMediaFile;
8.3.2
Self Field
One special field that is created by
default or you can add manually in
persistent fields is a field named "Self". It is an
representing the object associated with the current record. It's useful for
following code, both lines are equivalent (if there is a current record):
Customer1 := AureliusDataset1.Current<TCustomer>;
Customer2 :=
AureliusDataset1.EntityFieldByName( 'Self' ).AsEntity<TCustomer>;
// Customer1 = Customer2
8.3.3
Sub-Property Fields
You can access properties of associated objects (sub-properties) through
TAureliusDataset. Suppose you have a class like this:
TCustomer =
class
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// <snip>
public property
Id: Integer
read
FId
write
FId;
property
Name:
string read
FName
write
FName;
property
Country: TCountry
read
FCountry
write
FCountry;
end
;
You can access properties of Country object using dots:
AureliusDataset1.FieldByName( 'Country.Name' ).AsString :=
'Germany' ;
As you might have noticed, sub-property fields can not only be read, but also written to. There is not a limit for level access, which means you can have fields like this:
CountryName :=
AureliusDataset1.FieldByName( 'Invoice.Customer.Country.Name' ).As
String;
It's important to note that sub-property fields are not created by default when using
default fields . In the example of TCustomer class above, only field
"Country" will be created by default, but not "Country.Name" or any of its subproperties. To use a sub-property field, you must manually add the field to the dataset before opening it. Just like any other TDataset, you do that at designtime, or at runtime:
with
TStringField.Create(Self)
do begin
FieldName := 'Country.Name' ;
Dataset := AureliusDataset1;
end
;
8.3.4
Entity Fields (Associations)
Entity Fields are fields that maps to an object property in a container object.
In other words, entity fields represent associations in the object. Consider the following class:
TCustomer =
class
// <snip>
public property
Id: Integer
read
FId
write
FId;
property
Name:
string read
FName
write
FName;
property
Country: TCountry
read
FCountry
write
FCountry;
end
;
By default, TAureliusDataset will create fields "Id" and "Name" (scalar fields) and "Country" (entity field). An entity field is just a field of type
TAureliusEntityField that holds a reference to the object itself. Since Delphi DB library doesn't provide a field representing an object pointer (which makes sense), this new field type is provided by TMS Aurelius framework for you to manipulate the object reference.
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The TAureliusEntityField is just a TVariantField descendant with an additional
AsObject property, and an addition generic AsEntity<T> function that you can use to better manipulate the field content. To access such properties, you can just cast the field to TAureliusEntityField, or use
TAureliusDataset.EntityFieldByName method.
Please note that the entity field just represents an object reference. It's useful for
lookup fields and to programatically change the object reference in the
property, but it's not useful (and should not be used) for visual binding, like a
TDBGrid or to be edited in a TDBEdit, since its content is just a pointer to the object. To visual bind properties of associated objects, use
.
The following code snippets are examples of how to use the entity field.
// following lines are equivalent and illustrates how to set an association through the dataset
AureliusDataset1.EntityFieldByName( 'Country' ).AsObject :=
TCountry.Create;
(AureliusDataset1.FieldByName( 'Country' )
as
TAureliusEntityField).AsObject := TCountry.Create;
Following code shows how to retrieve the value of an association property using the dataset field:
Country :=
AureliusDataset1.EntityFieldByName( 'Country' ).AsEntity<TCountry>
;
8.3.5
Dataset Fields (Many-Valued Associations)
Dataset fields represent collections in a container object. In other words, dataset fields represent many-valued associations in the object. Consider the following class:
TInvoice =
class
// <snip>
public property
Id: Integer
read
FId
write
FId;
property
Items: TList<TInvoiceItem>
read
GetItems;
end
;
The field "Items" is expected to be a TDatasetField, and represents all objects
(records) in the Items collection. Different from
entity fields , you don't access
a reference to the list itself, using the dataset field.
In short, you can use the TDatasetField to build master-detail relationships.
You can have, for example, a TDBGrid linked to a dataset representing a list of
TInvoice objects, and a second TDBGrid linked to a dataset representing a list of TInvoiceItem objects. To link the second dataset (invoice items) to the first
(invoices) you just need to set the DatasetField property of the second
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dataset. This will link the detail dataset to the collection of items in the first dataset. You can do it at runtime or design-time.
The following code snippet illustrates better how to link two datasets using the dataset field. It's worth to note that these dataset fields work as a regular
TDatasetField. For a better understanding of how a TDatasetField works, please refer to Delphi documentation.
InvoiceDataset.SetSourceList(List);
InvoiceDataset.Manager := Manager1;
InvoiceDataset.Open;
ItemsDataset.DatasetField := InvoiceDataset.FieldByName( 'Items' )
as
TDatasetField;
ItemsDataset.Open;
Note that by default there is no need to set the
datasets. There is a TAureliusDataset.ParentManager proeprty which defaults to true, that indicates that the Manager of the dataset will be same as the
Manager of the parent dataset (which is the dataset of the linked
DatasetField). In this case, whenever you Post or Delete a record in the detail dataset, the detail object will be immediately persisted in the database.
In case you don't want this behavior (for example, you want the details dataset to save objects in memory and only when the master object is saved you have details being saved at once), you can explicitly set the Manager property of the details dataset to nil. This will automatically set the
ParentManager property to false:
InvoiceDataset.SetSourceList(List);
InvoiceDataset.Manager := Manager1;
// Set Manager to nil so only save items when InvoiceDataset is posted.
// ItemsDataset.ParentManager will become false
ItemsDataset.Manager :=
nil
;
InvoiceDataset.Open;
As with any master-detail relationship, you can add or remove records from the detail/nested dataset, and it will add/remove items from the collection:
ItemsDataset.Append;
ItemsDataset.FieldByName( 'ProductName' ).AsString := 'A' ;
ItemsDataset.FieldByName( 'Price' ).AsCurrency := 1 ;
ItemsDataset.Post;
ItemsDataset.Append;
ItemsDataset.FieldByName( 'ProductName' ).AsString := 'B' ;
ItemsDataset.FieldByName( 'Price' ).AsCurrency := 1 ;
ItemsDataset.Post;
8.3.6
Heterogeneous Lists (Inheritance)
When
providing objects to the dataset, the list provided might have objects
instances of different classes. This happens for example when you perform a
query . Suppose you have a class hierarchy which base class is
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TAnimal, and descendant classes are TDog, TMammal, TBird, etc.. When you perform a query like this:
Animals := Manager.Find<TAnimal>.List;
You might end up with a list of objects of different classes like TDog or TBird.
Suppose for example TDog class has a DogBreed property, but TBird does not.
Still, you need to create a field named "DogBreed" so you can display it in a grid or edit that property in a form.
TAureliusDataset allows you to create fields mapped to properties that might not exist in the object. Thus, you can create a persistent field named
"DogBreed", or you can change the
base class of the dataset to TDog so that
the default fields will include a field named "DogBreed".
To allow this feature to work well, when such a field value is requested and the property does not exist in the object, TAureliusDataset will not raise any error.
Instead, the field value will be null. Thus, if you are listing the objects in a dbgrid, for example, a column associated with field "DogBreed" will display the property value for objects of class TDog, but will be empty for objects of class
TBird, for example. Please note that this behavior only happens when reading the field value. If you try to set the field value and the property does not exist, an error will be raised when the record is posted. If you don't change the field value, it will be ignored.
Also note that the base class is used to create a new object instance when inserting new records (creating objects). The following code illustrates how to use a dataset associated with a TList<TAnimal> and still creating two different object types:
Animals := Manager.FindAll<TAnimal>;
DS.SetSourceList(Animals);
// base class is TAnimal
DS.ObjectClass := TDog;
// not base is class is TDog
DS.Open;
DS.Append;
DS.FieldByName( 'Name' ).AsString := 'Snoopy' ;
DS.FieldByName( 'DogBreed' ).AsString := 'Beagle' ;
DS.Post;
// Create a new TDog instance
DS.Append;
DS.ObjectClass := TBird;
// change base class to TBird
DS.FieldByName( 'Name' ).AsString := 'Tweetie' ;
DS.Post;
// Create a new TBird instance. DogBreed field is ignored
8.3.7
Enumeration Fields
Fields that relate to an enumerated type are integer fields that hold the ordinal value of the enumeration. Example:
type
TSex = (tsMale, tsFemale);
TheSex := TSex(DS.FieldByName( 'Sex' ).AsInteger);
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DS.FieldByName( 'Sex' ).AsInteger := Ord(tsFemale);
Alternatively, you can use the sufix ".EnumName" after the property name so you can read and write the values in string format (string fields)
SexName := DS.FieldByName( 'Sex.EnumName' ).AsString;
DS.FieldByName( 'Sex.EnumName' ).AsString := 'tsFemale' ;
8.3.8
Fields for Projection Values
When using
in
queries , the result objects might be objects of type
TCriteriaResult . Such object has the content of projections available in the
Values property. TAureliusDataset treats such values as fields, so you can define a field for each projection value. Since TAureliusDataset cannot tell in advance what are the available fields, to use such scenario you must previously define the persistent fields for each aliased projection. The following code snippet illustrates how you can use projection values in TAureliusDataset.
with
TStringField.Create(Self)
do begin
FieldName := 'CountryName' ;
Dataset := AureliusDataset1;
Size := 50 ;
end
;
with
TIntegerField.Create(Self)
do begin
FieldName := 'Total' ;
Dataset := AureliusDataset1;
end
;
// Retrieve number of customers grouped by country
AureliusDataset1.SetSourceCriteria(
Manager.Find<TCustomer>
.Select(TProjections.ProjectionList
.Add(TProjections.Group( 'Country' ).As_( 'CountryName' ))
.Add(TProjections.Count( 'Id' ).As_( 'Total' ))
)
.AddOrder(TOrder.Asc( 'Total' ))
);
// Retrieve values for the first record: country name and number of customers
FirstCountry :=
AureliusDataset1.FieldByName( 'CountryName' ).AsString;
FirstTotal := AureliusDataset1.FieldByName( 'Total' ).AsInteger;
Note: The TCriteriaResult objects provided to the dataset might be automatically destroyed when the dataset closes, depending on how you
provide objects to the dataset . If you use SetSourceCursor or
SetSourceCriteria, they are automatically destroyed. This is because since the objects are fetched automatically by the dataset, it manages it's life-cycle.
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When you use SetSourceList or SetSourceObject, they are not destroyed and you need to do it yourself.
8.4
Modifying Data
Modifying data with TAureliusDataset is just as easy as with any TDataset component. Call Edit, Insert, Append methods, and then call Post to confirm or
Cancel to rollback changes.
It's worth note that TAureliusDataset load and save data from and to the
objects in memory. It means when a record is posted, the underlying associated object has its properties updated according to field values. However the object is not necessarily persisted to the database. It depends on if the
Manager property is set, or if you have set event handlers for object persistence, as illustrated in code below.
// Change Customer1.Name property
DS.Close;
DS.SetSourceObject(Customer1);
DS.Open;
DS.Edit;
DS.FieldByName( 'Name' ).AsString := 'John' ;
DS.Post;
// Customer1.Name property is updated to "John".
// Saving on database depends on setting Manager property
// or setting OnObjectUpdate event handler
The following topics explain some more details about modifying data with
TAureliusDataset.
8.4.1
New Objects When Inserting Records
When you insert new records, TAureliusDataset will create new object instances and add them to the underlying object list
The object might be created when the record enters insert state (default) or only when you post the record (if you set
TAureliusDataset.CreateObjectOnPost property to true). The class of object being created is specified by the base class (either retrieved from the list of objects or manually using ObjectClass property). See
topic for more details.
In the following code, a new TCustomer object will be created when Append is called (if you call Cancel the object will be automatically destroyed):
Customers := TObjectList<TCustomer>.Create;
DS.SetSourceList(Customer);
// base class is TCustomer
DS.Open;
DS.Append;
// Create a new TCustomer instance
DS.FieldByName( 'Name' ).AsString := 'Jack' ;
DS.Post;
// Destroy Customers list later!
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If you set CreateObjectOnPost to true, the object will only be created on Post.
Customers := TObjectList<TCustomer>.Create;
DS.SetSourceList(Customer);
// base class is TCustomer
DS.Open;
DS.Append;
DS.FieldByName( 'Name' ).AsString := 'Jack' ;
DS.Post;
// Create a new TCustomer instance
// Destroy Customers list later!
Setting the base class manually is also important if you are using
heterogeneous lists and want to create instances of different classes when
posting records, depending on an specific situation.
Alternatively, you can set OnCreateObject event handler. This event is called when the dataset needs to create the object, and the event type declaration is below:
type
TDatasetCreateObjectEvent =
procedure
(Dataset: TDataset;
var
NewObject: TObject)
of object
;
//<snip>
property
OnCreateObject: TDatasetCreateObjectEvent;
If the event handler sets a valid object into NewObject parameter, the dataset will not create the object. If NewObject is unchanged (remaining nil), then a new object of the class specified by the base class is created internally.
Here is an example of how to use it:
procedure
TForm1.AureliusDataset1CreateObject(Dataset:
TDataset;
var
NewObject: TObject);
begin
NewObject := TBird.Create;
end
;
//<snip>
AureliusDataset1.OnCreateObject :=
AureliusDataset1CreateObject;
AureliusDataset1.Append;
// a TBird object named "Tweetie" will be created here
AureliusDataset1.FieldByName( 'Name' ).AsString := 'Tweetie' ;
AureliusDatase1.Post;
A final note: after Post, objects created by TAureliusDataset are not destroyed anymore. See
Objects Lifetime Management for more information.
8.4.2
Manager Property
When posting records, object properties are updated, but are not persisted to the database, unless you
for persistence, or set Manager property. If you set the Manager property to a valid TObjectManager object, then when records are posted or deleted, TAureliusDataset will use the specified manager to
persist the objects to the database, either saving,
updating or removing the objects.
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Customers := TAureliusDataset.Create(Self);
CustomerList := TList<TCustomer>.Create;
Manager := TObjectManager.Create(MyConnection);
try
Customers.SetSourceList(CustomerList);
Customers.Open;
Customers.Append;
Customers.FieldbyName( 'Name' ).AsString := 'Jack' ;
// On post, a new TCustomer object named "Jack" is created, but not saved to database
Customers.Post;
// Now set the manager
Customers.Manager := Manager;
Customers.Append;
Customers.FieldbyName( 'Name' ).AsString := 'John' ;
// From now on, any save/delete operation on dataset will be reflected on database
// A new TCustomer object named "John" will be created, and
Manager.Save
// will be called to persist object in database
Customers.Post;
// Record is deleted from dataset and object is removed from database
Customers.Delete;
finally
Manager.Free;
Customers.Free;
CustomerList.Free;
end
;
In summary: if you want to manipulate objects only in memory, do not set
Manager property. If you want dataset changes to be reflected in database, set Manager property or use
.
Please refer to the topic using
Dataset Fields to learn how the Manager
property is propagated to datasets which are linked to dataset fields.
8.4.3
Objects Lifetime Management
TAureliusDataset usually does not manage any object it holds, either the entity objects itself, the list of objects that you pass in SetSourceList when
providing objects to it, or the objects it created automatically when
inserting new records . So you must be sure to destroy all of them when needed! The only
two exceptions are described at the end of this topic.
Even when deleting records, the object is not destroyed (if no Manager is attached). The following code causes a memory leak:
Customers := TAureliusDataset.Create(Self);
CustomerList := TList<TCustomer>.Create;
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Customers.SetSourceList(CustomerList);
Customers.Open;
Customers.Append;
Customers.FieldbyName( 'Name' ).AsString := 'Jack' ;
// On post, a new TCustomer object named "Jack" is created, but not saved to database
Customers.Post;
// Record is deleted from dataset, but object is NOT DESTROYED
Customers.Delete;
finally
Manager.Free;
Customers.Free;
CustomerList.Free;
end
;
In code above, a new object is created in the Post, but when record is deleted, object is not destroyed, although it's removed from the list.
But, be aware that the
itself
you set the
Manager property of the dataset, then records being saved will
cause objects to be saved or updated by the manager, meaning they will be managed by it. It works just as any object manager. So usually you would not need to destroy objects if you are using a TObjectManager associated with the dataset (but you would still need to destroy the TList object holding the objects). But just know that they are being managed by the TObjectManager object, not by the TAureliusDataset component itself.
Exceptions
There are only two exceptions when objects are destroyed by the dataset:
1. A record in Insert state is not Posted.
When you Append a record in the dataset, an object is created (
CreateObjectsOnPost property is set to true ). If you then Cancel the inserting
of this record, the dataset will silently destroy that object.
2. When objects of type
TCriteriaResult are passed using SetSourceCursor or
In this case the objects are destroyed by the dataset.
8.4.4
Manual Persistence Using Events
To properly persist objects to the database and manage them by properly destroying when needed, you would usually use the
and associate a TObjectManager object to the dataset.
Alternatively, you can also use events for manual persistence and management. Maybe you just want to keep objects in memory but need to destroy them when records are deleted, so you can use OnObjectRemove event. Or maybe you just want to hook a handler for the time when an object is updated and perform additional operations.
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The following events for handling objects persistence are available in
TAureliusDataset, and all of them are of type TDatasetObjectEvent:
type
TDatasetObjectEvent =
procedure
(Dataset: TDataset; AObject:
TObject)
of object
;
//<snip>
property
OnObjectInsert: TDatasetObjectEvent;
property
OnObjectUpdate: TDatasetObjectEvent;
property
OnObjectRemove: TDatasetObjectEvent;
OnObjectInsert event is called when a record is posted after an Insert or
Append operation, right after the object instance is created.
OnObjectUpdate event is called when a record is posted after an Edit operation.
OnObjectRemove event is called when a record is deleted.
In all events, the AObject parameter related to the object associated with the current record.
Note that if one of those event handlers are set, the object manager specified in
will be ignored and not used. So if for example you set an event handler for OnObjectUpdate event, be sure to persist it to the database if you want to, because Manager.Update will not be called even if Manager property is set.
8.5
Locating Records
TAureliusDataset supports usage of Locate method to locate records in the dataset. Use it just as with any regular TDataset descendant:
Found := AureliusDataset1.Locate( 'Name' , 'mi' ,
[loCaseInsensitive, loPartialKey]);
You can perform locate on
entity fields . Just note that since entity fields hold a
reference to the object itself, you just need to pass a reference in the locate method. Since objects cannot be converted to variants, you must typecast the reference to an Integer or IntPtr (Delphi XE2 and up).
{$IFDEF DELPHIXE2}
Invoices.Locate( 'Customer' , IntPtr(Customer), []);
{$ELSE}
Invoices.Locate( 'Customer' , Integer(Customer), []);
{$ENDIF}
The customer object must be the same. Even if Customer object has the same
Id as the object in the dataset, if the object references are not the same,
Locate will fail. Alternatively, you can also search on
Found := Invoices.Locate( 'Customer.Name' , Customer.Name, []);
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8.6
In this case, the record will be located if the customer name matches the specified value, regardless if object references are the same or not.
You can also search on
calculated and lookup fields .
Calculated Fields
You can use calculated fields in TAureliusDataset the same way with any other dataset. Note that when calculating fields, you can use regular
Dataset.FieldByName approach, or you can use Current<T> property and access the object properties directly.
procedure
TForm1.AureliusDataset1CalcFields(Dataset: TDataset);
begin if
AureliusDataset1.FieldByName( 'Birthday' ).IsNull
then
AureliusDataset1.FieldByName( 'BirthdayText' ).AsString :=
'not specified'
else
AureliusDataset1.FieldByName( 'BirthdayText' ).AsString :=
DateToStr(AureliusDataset1.FieldByName( 'Birthday' ).AsDateTime);
case
AureliusDataset1.Current<TCustomer>.Sex
of
tsMale:
AureliusDataset1.FieldByName( 'SexDescription' ).AsString
:= 'male' ;
tsFemale:
AureliusDataset1.FieldByName( 'SexDescription' ).AsString
:= 'female' ;
end
;
end
;
8.7
Lookup Fields
You can use lookup fields with TAureliusDataset, either at design-time or runtime. Usage is not different from any TDataset.
One thing it's worth note, though, is how to use lookup field for
, which is probably the most common usage. Suppose you have a
TInvoice class with a property Customer that is an association to a TCustomer class. You can have two datasets with TInvoice and TCustomer data, and you want to create a lookup field in Invoices dataset to lookup for a value in
Customers dataset, based on the value of Customer property.
Since "Customer" is an entity field in Invoices dataset, you need to lookup for its value in the Customers dataset using the
"Self" field , which represents a
reference to the TCustomer object in Customers dataset. The following code illustrates how to create a lookup field in Invoices dataset to lookup for the customer name based on "Customer" field:
// Invoices is a dataset which data is a list of TInvoice objects
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// Customers is dataset which data is a list of TCustomer objects
// Create the lookup field in Invoices dataset
LookupField := TStringField.Create(Invoices.Owner);
LookupField.FieldName := 'CustomerName' ;
LookupField.FieldKind := fkLookup;
LookupField.Dataset := Invoices;
LookupField.LookupDataset := Customers;
LookupField.LookupKeyFields := 'Self' ;
LookupField.LookupResultField := 'Name' ;
LookupField.KeyFields := 'Customer' ;
Being a regular lookup field, this approach also works with componentes like
TDBLookupComboBox and TDBGrid. It would display a combo with a list of customer names, and will allow you to change the customer of TInvoice object by choosing the item in combo (the field "Customer" in Invoices dataset will be updated with the value of field "Self" in Customers dataset).
8.8
Filtering
TAureliusDataset supports filtering of records by using regular TDataset.Filtered
property and TDataset.OnFilterRecord event. It works just as any TDataset descendant. Note that when filtering records, you can use regular
Dataset.FieldByName approach, or you can use Current<T> property and access the object properties directly.
procedure
TForm1.DatasetFilterRecord(Dataset: TDataset;
var
Accept: boolean);
begin
Accept :=
(Dataset.FieldByName( 'Name' ).AsString = 'Toby' )
or
(TAureliusDataset(Dataset).Current<TAnimal>
is
TMammal);
end
;
//<snip>
begin
AureliusDataset1.SetSourceList(Animals);
AureliusDataset1.Open;
AureliusDataset1.OnFilterRecord := DatasetFilterRecord;
AureliusDataset1.Filtered := True;
end
;
8.9
Design-time Support
TAureliusDataset is installed in Delphi component palette and can be used at design-time and as any TDataset component you can set its fields using fields editor, specify master-detail relationships by setting DatasetField property to a
lookup fields , among other common TDataset tasks.
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However, creating fields manually might be a boring task, especially if you have a class with many properties and need to create many fields manually. So
TAureliusDataset provides a design-time menu option named "Load Field
Definitions..." (right-click on the component), which allows you to load a class from a package and create the field definitions from that class.
A dialog appears allowing you to choose a class to import the definitions from.
Note that the classes are retrieving from available packages. By default, classes from packages installed in the IDE are retrieved. If you want to use a package that is not installed, you can add it to the packages list. So, for a better design-time experience with TAureliusDataset, create a package with
all your entity classes, compile it, and load it in this dialog.
The packages in the list are saved in the registry so you can reuse it whenever you need. To remove the classes of a specified package from the combo box, just uncheck the package. The package will not keep loaded: when the dialog closes, the package is unloaded from memory.
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Note that the dialog will create fill the FieldDefs property, not create field components in the fields editor. The FieldDefs behaves as if the field definitions are being retrieved from a database. You would still need to create the field components, but now you can use the FieldDefs to help you, so you can use
"Add All Fields" or "Add Field..." options from the fields editor popup menu. The
FieldDefs property is persisted in the form so you don't need to reload the package in case you close the form and open it again. That's its only purpose, and they are not used at runtime.
8.10
Other Properties And Methods
List of TAureliusDataset methods and properties not coverered by other topics in this
Properties
Name
property
CreateSelfField:
Boolean property
DefaultsFromObject
: Boolean
Description
When True (default), the dataset will include the Self field in the list of default fieldsdefs. If False, the field will not be created.
When True, brings field default values with object state. When inserting a new record in TAureliusDataset, all fields come with null values by default
(DefaultsFromObject is False). By setting this property to True, default (initial) value of the fields will come from the property values of the underlying object.
property
IncludeUnmappedOb jects: Boolean
When True, the dataset will also create field definitions for object (and lists) properties that are not mapped. In other words, you can view/edit transient object properties. The default is False which means only
Aurelius associations will be visible.
propery
SubpropsDepth:
Integer property
SyncSubProps:
Boolean
Allows automatic loading of subproperty fields. When loading field definitions for TAureliusDataset at
, or when opening the TAureliusDataset without
persistent fields, one TField for each property in object will be created. By increasing SubpropsDepth to 1 or more, TAureliusDataset will also automatically include subproperty fields for each property in each association, up to the level indicated by
SubpropsDepth. For example, if SubpropsDepth is 1, and there is an association field named "Customer", the dataset will also create fields like "Customer.Name",
"Customer.Birthday", etc.. Default is 0 (zero).
Allows automatic updating of associated fields. When an entity field (e.g., "Customer") of the TAureliusDataset component is modified, all the
"Customer.Name", "Customer.Birthday") will be automatically updated with new values if this property is set to True. Default is False.
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Chapter
IX
Distributed
Applications
TMS Aurelius Documentation
9 Distributed Applications
You can build distributed applications using Aurelius. When
, you can specify any class ancestor, and you can define which fields and properties will be mapped or not. This gives you flexibility to use almost any framework for building distributed applications - even if that framework requires that the classes need to have specific behavior (like inheriting from a specific base class, for example).
Still, Aurelius provides several mechanisms and classes that make building distributed applications even easier. The following topics describe features for building distributed applications using Aurelius.
JSON - JavaScript Object Notation
9.1
JSON - JavaScript Object Notation
When building distributed applications, you need to transfer your objects between peers. Usually to transfer objects you need to convert them (marshal) to a format that you can send through your communication channel. Currently one of the most popular formats for that is the JSON format. It's simple, text representation, that can easily be parsed, lightweight, and portable. You can build your server using Aurelius, retrieve your objects from database, convert them to JSON, send the objects through any communication channel to client, and from the client, you can convert the JSON back to an Aurelius object.
Since it's a portable format, your client doesn't even need to be a Delphi application using Aurelius - you can use a JavaScript client, for example, that fully supports the JSON format, or any other language.
To converting Aurelius objects to JSON you can use one of the
Serializer := TDataSnapJsonSerializer.Create;
try
JsonValue := Serializer.ToJson(Customer);
finally
Serializer.Free;
end
;
To convert a JSON notation back to an Aurelius object, you can use one of the
available JSON deserializers :
Deserializer := TDataSnapJsonDeserializer.Create;
try
Customer := Deserializer.FromJson<TCustomer>(JsonValue);
finally
Deserializer.Free;
end
;
The following topics describes in more details how to better use the JSON with
Aurelius.
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9.1.1
Available Serializers
Aurelius uses an open architecture in JSON support that allows you to use any framework for parsing and generating the JSON representation. This makes it easy to use your preferred framework for building distributed applications and use legacy code. For example, if you are using DataSnap, Aurelius provides the
DataSnap serializer that converts the object to a TJsonValue object which holds the JSON representation structure. You can use the TJsonValue directly in a DataSnap server to send JSON to the client. Other frameworks use different objects for JSON representation (or simply string format) so you can use any you want.
The following table lists the currently available JSON serializer/deserializer classes in Aurelius, what framework they use, and what is the base type that is uses for JSON representation:
Fram ework
Serializer class
Deserializer class
JSON
Class
Declared in unit
Vendor Site
DataS nap
TDataSnapJs onSerializer
Super
Object
TSuperObjec tJsonSerialize r
TDataSnapJso nDeserializer
TJsonVal ue
Aurelius.Jso
n.DataSnap
TSuperObject
JsonDeserializ er
ISuperO bject
Aurelius.Jso
n.SuperObje
ct
Delphi Native http:// code.google.com/ p/superobject/
All serializers have a ToJson method that receives an object and returns the type specified by the JSON Class in the table above.
All deserializers have a generic FromJson method that receives the type specified by JSON class in the table above and returns the type specified in the generic parameter.
Both serializer and deserializer need a reference to a
object to work with. You can pass the object in the Create constructor when creating a serializer/deserializer, or you can use the method with no parameter to use the
default mapping setup . The following code snippets illustrate different ways
of using the serializers:
Serializing/Deserializing an Aurelius object using DataSnap JSON classes and default mapping setup:
uses
{...}
, Aurelius.Json.DataSnap;
var
Serializer: TDataSnapJsonSerializer;
Deserializer: TDataSnapJsonDeserializer;
Customer: TCustomer;
AnotherCustomer: TCustomer;
JsonValue: TJsonValue;
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{...}
Serializer := TDataSnapJsonSerializer.Create;
Deserializer := TDataSnapJsonDeserializer.Create;
try
JsonValue := Serializer.ToJson(Customer);
AnotherCustomer :=
Deserializer.FromJson<TCustomer>(JsonValue);
finally
Serializer.Free;
Deserializer.Free;
end
;
{...}
end
;
Serializing/Deserializing an Aurelius object using SuperObject and custom mapping setup:
uses
{...}
, Aurelius.Json.SuperObject;
var
Serializer: TSuperObjectJsonSerializer;
Deserializer: TSuperObjectJsonDeserializer;
Customer: TCustomer;
AnotherCustomer: TCustomer;
SObj: ISuperObject;
CustomMappingExplorer: TMappingExplorer;
begin
{...}
Serializer :=
TSuperObjectJsonSerializer.Create(CustomMappingExplorer);
Deserializer :=
TSuperObjectJsonDeserializer.Create(CustomMappingExplorer);
try
SObj := Serializer.ToJson(Customer);
AnotherCustomer := Deserializer.FromJson<TCustomer>(SObj);
finally
Serializer.Free;
Deserializer.Free;
end
;
{...}
end
;
9.1.2
Serialization behavior
Aurelius maps each relevant field/attribute to the JSON representation, so that the JSON holds all (and only) relevant information to represent an object state.
So for example, a class mapped like this:
[Entity]
[Table( 'ARTISTS' )]
[Id( 'FId' , TIdGenerator.IdentityOrSequence)]
TArtist =
class
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[Column( 'ID' , [TColumnProp.Unique, TColumnProp.Required,
TColumnProp.NoUpdate])]
FId: Integer;
FArtistName:
string
;
FGenre: Nullable<
string
>;
function
GetArtistName:
string
;
procedure
SetArtistName(
const
Value:
string
);
public property
Id: integer
read
FId;
[Column( 'ARTIST_NAME' , [TColumnProp.Required], 100 )]
property
ArtistName:
string read
GetArtistName
write
SetArtistName;
[Column( 'GENRE' , [], 100 )]
property
Genre: Nullable<
string
>
read
FGenre
write
FGenre;
end
; will generate the following JSON representation:
{
"$type": "Artist.TArtist",
"$id": 1,
"FId": 2,
"ArtistName": "Smashing Pumpkins",
"Genre": "Alternative"
}
Note that fields FId and properties ArtistName and Genre are mapped, and so are the ones that appear in the JSON format. Aurelius includes extra meta fields (starting with $) for its internal use that will make it easy to later deserialize the object.
dynamic properties are automatically
handled by the serializer/deserializer.
Blob fields
Content of blobs are converted into a base64 string so it can be properly deserialized back to a binary format (Data field is truncated in example below):
{
"$type": "Images.TImage",
"$id": 1,
"FId": 5,
"ImageName": "Landscape",
"Data":
"TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ
1dCBieSB0aGlz...
}
If blobs are set to be lazy and they are not loaded, then they will not be fully sent in JSON representation, but only a meta information that will allow you to load it later. See more at
Associations
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If the object being serialized has associations and/or many-valued associations, those objects are also serialized in the JSON. The following example shows a serialization of a class TSong which has properties Album,
Artist and SongFormat that points to other objects:
{
"$type": "Song.TSong",
"$id": 1,
"FAlbum": {
"$proxy": "single",
"key": 2,
"class": "TMediaFile",
"member": "FAlbum"
},
"MediaName": "Taxman2",
"Duration": 230,
"FId": 1,
"FArtist": {
"$proxy": "single",
"key": 1,
"class": "TMediaFile",
"member": "FArtist"
},
"FileLocation": "",
"SongFormat": {
"$type": "SongFormat.TSongFormat",
"$id": 2,
"FId": 1,
"FormatName": "MP3"
}
}
If the association is marked as lazy-loading and is not load yet, then they will not be included in JSON representation, but instead a meta information will be included for later loading the value. In the example above, FAlbum and FArtist were defined as proxies and were not loaded, so the object they hold is a proxy meta information. On the other hand, SongFormat property is loaded and the whole TSongFormat object is serialized in it. For more information on lazyloading, see
9.1.3
Lazy-Loading with JSON
An object being serialized might have
and
many-valued associations defined to be
lazy-loaded . When that is the case and the proxies
are not loaded yet, the associated objects are not serialized, but instead, an object with metadata for that proxy is serialized instead. Take a look at the following example (irrelevant parts of the real JSON notation were removed):
{
"$type": "Song.TSong",
"$id": 1,
"FId": 1,
"FAlbum": {
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"$proxy": "single",
"key": 2,
"class": "TMediaFile",
"member": "FAlbum"
},
"FileLocation": ""
}
In that example, TSong has a FAlbum field of type Proxy<TAlbum>. The song being serialized doesn't have the FAlbum field loaded, so instead of the actual
TAlbum object to be serialized, a proxy object is serialized instead. The proxy object is indicated by the presence of the meta property "$proxy", which indicates if it's a proxy for a single object or a list.
How does the deserializer handle this? All JSON deserializers have a property
ProxyLoader which points to an interface of type IJsonProxyLoader declared like this:
IJsonProxyLoader =
interface function
LoadProxyValue(ProxyInfo: IProxyInfo): TObject;
end
; while the IProxyInfo object is declared like this (in unit Aurelius.Types.Proxy):
IProxyInfo =
interface function
ProxyType: TProxyType;
function
ClassName:
string
;
function
MemberName:
string
;
function
Key: Variant;
end
;
When the TSong object in the previous example is deserialized, an internal proxy is set automatically in the FAlbum field. When the Album property of
Song object is read, the proxy calls the method LoadProxyValue of the
IJsonProxyLoader interface. So for the object to be loaded by the proxy, you must provide a valid IJsonProxyLoader interface in the deserializer so that you can load the proxy and pass it back to the engine. The easiest way to create an IJsonProxyLoader interface is using the TJsonProxyLoader interface object provided by Aurelius.
The following code illustrates how to do it:
Deserializer := TDataSnapJsonDeserializer.Create;
try
Deserializer.ProxyLoader := TJsonProxyLoader.Create(
function
(ProxyInfo: IProxyInfo): TObject
var
Serializer: TDataSnapJsonSerializer;
Deserializer: TDataSnapJsonDeserializer;
JsonObject: TJsonValue;
begin
Serializer:= TDataSnapJsonSerializer.Create;
Deserializer := TDataSnapJsonDeserializer.Create;
try
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JsonObject :=
DatasnapClient.RemoteProxyLoad(Serializer.ToJson(ProxyInfo));
Result := Deserializer.FromJson(JsonObject, TObject);
finally
Deserializer.Free;
Serializer.Free;
end
;
end
);
Song := Deserializer.FromJson<TSong>(JsonValueWithSong);
finally
Deserializer.Free;
end
;
// At this point, Song.Album is not loaded yet
// When the following line of code is executed (Album property is read)
// then the method specified in the ProxyLoader will be executed and
// Album will be loaded
Album := Song.Album;
AlbumName := Album.Name; you can safely destroy the deserializer after the object is loaded, since the reference to the proxy loader will be in the object itself. It's up to you how to implement the ProxyLoader. In the example above, we are assuming we have a client object with a RemoteProxyLoad method that calls a server method passing the ProxyInfo data as json format. In the server, you can easily implement such method just by receiving the proxy info format, converting it back to IProxyInfo interface and then calling TObjectManager.ProxyLoad
method:
// This methos assumes that Serializer, Deserializer and
ObjectManager objects
// are already created by the server
function
TMyServerMethods.RemoteProxyLoad(JsonProxyInfo:
TJsonValue): TJsonValue;
var
ProxyInfo: IProxyInfo;
begin
ProxyInfo :=
Deserializer.ProxyInfoFromJson<IProxyInfo>(JsonProxyInfo);
Result :=
Serializer.ToJson(ObjectManager.ProxyLoad(ProxyInfo));
end
;
Lazy-Loading Blobs
In an analog way, you can lazy-load blobs with Json. It works exactly the same as loading associations. The deserializer has a property named Blob loader which points to an IJsonBlobLoader interface:
IJsonBlobLoader =
interface function
ReadBlob(BlobInfo: IBlobInfo): TArray<byte>;
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; and the IBlobInfo object is declared like this (in unit Aurelius.Types.Blob):
IBlobInfo =
interface function
ClassName:
string
;
function
MemberName:
string
;
function
Key: Variant;
end
; and you can use TObjectManager.BlobLoad method at server side.
9.1.4
Memory Management with JSON
When deserializing a JSON value, objects are created by the deserializer. You must be aware that not only the main object is created, but also the associated objects, if it has associations. For example, if you deserialize an object of class TSong, which has a property TSong.Album, the object TAlbum will be also serialized. Since you are not using an
memory for you, in theory you would have to destroy those objects:
Song := Deserializer.FromJson<TSong>(JsonValue);
{ do something with Song, then destroy it - including associations }
Song.Album.Free;
Song.Free;
You might imagine that if your JSON has a complex object tree, you will end up having to destroy several objects (what about Song.Album.AlbumType.Free, for example). To minimize this problem, deserializers have a property OwnsEntities that when enabled, destroys every object created by it (except lists). So your code can be built this way:
Deserializer := TDataSnapJsonDeserializer.Create;
Deserializer.OwnsEntities := true;
Song := Deserializer.FromJson<TSong>(JsonValue);
{ do something with Song, then destroy it - including associations }
Deserializer.Free;
// After the above line, Song and any other associated object
// created by the deserializer are destroyed
Alternatively, if you still want to manage objects by yourself, but want to know which objects were created by the deserializer, you can use OnEntityCreated event:
Deserializer.OnEntityCreated := EntityCreated;
procedure
TMyClass.EntityCreated(Sender: TObject; AObject:
TObject);
begin
// Add created object to a list for later destruction
FMyObjects.Add(AObject);
end
;
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In addition to OnEntityCreated event, the deserializer also provides Entities property which contains all objects created by it.
property
Entities: TEnumerable<TObject>;
Note about JSON classes created by serializer
You must also be careful when converting objects to JSON. It's up to you to destroy the class created by the serializer, if needed. For example:
var
JsonValue: TJsonValue;
begin
Value := DataSnapDeserializer.ToJson(Customer);
// Value must be destroyed later
In the previous example, Value is a TJsonValue object and it must be destroyed. Usually you will use DataSnap deserializer in a DataSnap application and in most cases where you use TJsonValue objects in DataSnap, the framework will destroy the object automatically. Nevertheless you must pay attention to situations where you need to destroy it.
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Chapter
X
Events
TMS Aurelius Documentation
10 Events
Aurelius provides an event system which you can use to receive callback notifications when some events occur, for example, an entity update or a item is included in a collection. This chapter explains how to use this event system and what events are available.
10.1
Using Events
Events in Aurelius are available in the Events property of the
object. Such property refers to a TManagerEvents (declared in unit
Aurelius.Events.Manager) object with several subproperties, each to them related to an event. For example, to access the OnInserted event of the default TMappingExplorer:
uses
{...}
, Aurelius.Mapping.Explorer, Aurelius.Events.Manager;
TMappingExplorer.
Default
.Events.OnInserted.Subscribe(
procedure
(Args: TInsertedArgs)
begin
// Use Args.Entity to retrieve the inserted entity
end
);
TMappingExplorer.
Default
.Events.OnUpdated.Subscribe(
procedure
(Args: TUpdatedArgs)
begin
// Use Args.Entity to retrieve the updated entity
end
);
In a less direct way, using method reference instead of anonymous method:
uses
{...}
, Aurelius.Mapping.Explorer, Aurelius.Events.Manager; procedure TSomeClass.MyInsertedProc(Args: TInsertedArgs); begin
// Use Args.Entity to retrieve the inserted entity
end;
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procedure TSomeClass.MyUpdatedProc(Args: TUpdatedArgs); begin
// Use Args.Entity to retrieve the updated entity
end; procedure TSomeClass.RegisterMyEventListeners;
var
Events: TManagerEvents;
begin
Events := TMappingExplorer.
Default
.Events;
Events.OnInserted.Subscribe(MyInsertedProc);
Events.OnUpdated.Subscribe(MyUpdatedProc);
end
;
The events are available in the TMappingExplorer object so the listeners will receive notifications about any event fired by any TObjectManager created that references the specified TMappingExplorer object. In other words, the events are "global" for that mapping explorer.
Listeners are method references that receive a single object as a parameter.
Such object has several properties containing relevant information about the event, and differ for each event type. Names of event properties, method reference type and arguments follow a standard. The event property is named
"On<event>", method reference type is "T<event>Proc" and parameter object is "T<event>Args". For example, for the "Deleted" event, the respective names will be "OnDeleted", "TDeletedProc" and "TDeletedArgs".
All events in Aurelius are multicast events, which means you can add several events handlers (listeners) to the same event. When an event occurs, all listeners will be notified. This allows you to add a listener in a safe way, without worrying if it will replace an existing listener that might have been set by other part of the application. You should use Subscribe and Unsubscribe methods to add and remove listeners, respectively. Note that since listeners are method references, you must sure to unsubscribe the same reference you subscribed to:
var
LocalProc: TInsertedProc;
begin
LocalProc := MyInsertedProc;
Events.OnInserted.Subscribe(LocalProc);
{...}
Events.OnInserted.Unsubscribe(LocalProc);
end
;
Passing just the method name doesn't work work:
Events.OnInserted.Subscribe(MyInsertedProc);
{...}
Events.OnInserted.Unsubcribe(MyInsertedProc);
// this will NOT unsubscribe the previous subscription!
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10.2
OnInserting Event
Occurs right before an entity is inserted (create) in the database. Note that the event is fired for every entity that is about to be inserted. For example, a single
call might cause several entities to be inserted, due to
cascades defined in the associations . In this case the event will be fired
multiple times, one for each saved entity, even when the developer only called
Save once.
Example:
TMappingExplorer.
Default
.Events.OnInserting.Subscribe(
procedure
(Args: TInsertingArgs)
begin
// code here
end
);
TInsertingArgs Properties
Name Description
property Manager:
TBaseObjectManag er
The TObjectManager object which fired the event.
property Entity:
TObject
The entity about to be inserted.
property Master:
TMasterObjectValue
The parent object of the object being inserted. This property comes with a value in the case of list items
(ManyValuedAssociation) that don't have a reference back to parent (unidirectional). TMasterObjectValue has two relevant properties: "MasterObject" which is the instance of parent object, and "MasterAssocMember" which is the name of the list property the item being inserted belongs to (for example, "InvoiceItems").
10.3
OnInserted Event
Occurs right after an entity is inserted (create) in the database. Note that the event is fired for every entity inserted. For example, a single
call might cause several entities to be inserted, due to
the
associations . In this case the event will be fired multiple times, one for
each saved entity, even when the developer only called Save once.
Example:
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TMappingExplorer.
Default
.Events.OnInserted.Subscribe(
procedure
(Args: TInsertedArgs)
begin
// code here
end
);
TInsertedArgs Properties
Name Description
The TObjectManager object which fired the event.
property Manager:
TBaseObjectManag er property Entity:
TObject
The entity that was inserted property Master:
TMasterObjectValue
The parent object of the object being inserted. This property comes with a value in the case of list items
(ManyValuedAssociation) that don't have a reference back to parent (unidirectional). TMasterObjectValue has two relevant properties: "MasterObject" which is the instance of parent object, and "MasterAssocMember" which is the name of the list property the item being inserted belongs to (for example, "InvoiceItems").
10.4
OnUpdating Event
Occurs right before an entity is about to be updated in the database.
Example:
TMappingExplorer.
Default
.Events.OnUpdating.Subscribe(
procedure
(Args: TUpdatingArgs)
begin
// code here
end
);
TUpdatingArgs Properties
Name Description
property Manager:
TBaseObjectManag er
The TObjectManager object which fired the event.
property Entity:
TObject property
OldColumnValues:
The entity that is goint to be updated
Represents the old object state using column name/ value pairs. Don't confuse it with property names/
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TDictionary<string,
Variant> values. For example, if the object has a property named
"Name" that is mapped to a column database
"CUSTOMER_NAME", the dictionary will contain
"CUSTOMER_NAME" in the string key, and the respective value. Thus, associations are also represented by the foreign key column names/values.
property
NewColumnValues:
TDictionary<string,
Variant>;
Same as OldColumnValues, but contains the new state values. Comparing what has changed between
NewColumnValues and OldColumnValues will give you the names of the columns that will be updated in the database.
property
ChangedColumnNam es: TList<string>
Contains a list of names of all columns that will be updated in the UPDATE statement. property
RecalculateState:
Boolean
If you have changed any property value of the entity that is about to be updated, you need to set
RecalculateState to True to force Aurelius to recalculate the columns that were modified and update the object state in the manager cache. For better performance, leave it false if you haven't modified any property.
10.5
OnUpdated Event
Occurs right after an entity is updated in the database.
Example:
TMappingExplorer.
Default
.Events.OnUpdated.Subscribe(
procedure
(Args: TUpdatedArgs)
begin
// code here
end
);
TUpdatedArgs Properties
Name Description
property Manager:
TBaseObjectManag er
The TObjectManager object which fired the event.
property Entity:
TObject property
OldColumnValues:
TDictionary<string,
Variant>
The entity that was updated
Represents the old object state using column name/ value pairs. Don't confuse it with property names/ values. For example, if the object has a property named
"Name" that is mapped to a column database
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"CUSTOMER_NAME", the dictionary will contain
"CUSTOMER_NAME" in the string key, and the respective value. Thus, associations are also represented by the foreign key column names/values.
property
NewColumnValues:
TDictionary<string,
Variant>;
Same as OldColumnValues, but contains the new state values. Comparing what has changed between
NewColumnValues and OldColumnValues will give you the names of the columns that will be updated in the database.
property
ChangedColumnNam es: TList<string>
Contains a list of names of all columns that were updated in the UPDATE statement.
10.6
OnDeleting Event
Occurs right before an entity is about to be deleted from the database. Note that the event is fired for every entity deleted. For example, a single
call might cause several entities to be deleted, due to
cascades defined in the associations . In this case the event will be fired
multiple times, one for each deleted entity, even when the developer only called Remove once.
Example:
TMappingExplorer.
Default
.Events.OnDeleting.Subscribe(
procedure
(Args: TDeletingArgs)
begin
// code here
end
);
TDeletingArgs Properties
Name Description
property Manager:
TBaseObjectManag er
The TObjectManager object which fired the event.
property Entity:
TObject
The entity about to be deleted.
10.7
OnDeleted Event
Occurs right after an entity is deleted from the database. Note that the event is fired for every entity deleted. For example, a single
might cause several entities to be deleted, due to
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associations . In this case the event will be fired multiple times, one for each
deleted entity, even when the developer only called Remove once.
When the event is fired, the entity object is still a valid reference, but will be destroyed right after the event listener returns.
Example:
TMappingExplorer.
Default
.Events.OnDeleted.Subscribe(
procedure
(Args: TDeletedArgs)
begin
// code here
end
);
TDeletedArgs Properties
Name Description
The TObjectManager object which fired the event.
property Manager:
TBaseObjectManag er property Entity:
TObject
The deleted entity.
10.8
OnCollectionItemAdded Event
Occurs when an item is added to a collection, at database level. In other words, when the foreign key of an item entity is set to point to the parent entity.
Example:
TMappingExplorer.
Default
.Events.OnCollectionItemAdded.Subscribe(
procedure
(Args: TCollectionItemAddedArgs)
begin
// code here
end
);
Properties in TCollectionItemAddedArgs: property
Manager: TBaseObjectManager;
The TObjectManager object which fired the event.
property
Parent: TObject;
The parent entity which contains the collection where the item was added to.
property
Item: TObject;
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The item entity added to the collection
property
MemberName:
string
;
The member name (field or property) of the parent entity that holds the collection.
10.9
OnCollectionItemRemoved Event
Occurs when an item is removed from a collection, at database level. In other words, when the foreign key of an item entity is set to null (or to a different parent entity).
Example:
TMappingExplorer.
Default
.Events.OnCollectionItemRemoved.Subscrib
e(
procedure
(Args: TCollectionItemRemovedArgs)
begin
// code here
end
);
Properties in TCollectionItemRemovedArgs: property
Manager: TBaseObjectManager;
The TObjectManager object which fired the event.
property
Parent: TObject;
The parent entity which contains the collection where the item was removed from.
property
Item: TObject;
The item entity removed from the collection.
property
MemberName:
string
;
The member name (field or property) of the parent entity that holds the collection.
10.10
OnSqlExecuting Event
Occurs right before an SQL statement is executed.
Example:
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TMappingExplorer.
Default
.Events.OnSqlExecuting.Subscribe(
procedure
(Args: TSQLExecutingArgs)
begin
// code here
end
);
TSQLExecutingArgs Properties:
Name
SQL: string
Params:
TEnumerable<TDBP aram>
Description
The SQL statement that will be executed
A list of TDBParam objects used for the SQL statement execution. The TDBParam object has the properties
ParamName, ParamType and ParamValue.
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Chapter
XI
Advanced Topics
TMS Aurelius Documentation
11 Advanced Topics
Here we present some advanced topics about TMS Aurelius.
11.1
Global Configuration
TMS Aurelius has a single global class that has some properties for setting global configuration. This class is declared in unit Aurelius.Globals.Config, and to access the global configuration object, use TGlobalConfigs.GetInstance:
uses
Aurelius.Global.Config;
...
Configs := TGlobalConfigs.GetInstance;
The following properties are available in the TGlobalConfigs object:
property SimuleStatements: Boolean;
If true, all statements are not executed on the DBMS, but appear in the listeners.
property MaxEagerFetchDepth: Integer;
Indicates the maximum depth to load objects in eager loading
Beyond this depth, the objects still load in lazy mode.
property AutoSearchMappedClasses: Boolean;
If true, all classes declared in your application with [Entity] attribute are automatically added to the framework's MappedClasses.
Removed in version 2.0
: Use
instead.
property TightStringEnumLength: Boolean;
If true, in enumerations mapped to string columns with no length specified in the
attribute will generate the column length equal to the largest possible value of the enumeration. Otherwise, the length is
DefaultStringColWidth by default (when not specified in Column attribute).
property AutoMappingMode: TAutomappingMode;
Defines the automapping mode. Valid values are:
Off: No automatic mapping. Only elements with attributes are mapped.
ByClass: Automapping is done for classes marked with
Full: Full automapping over every registered class and
property AutoMappingDefaultCascade: TCascadeTypes; property AutoMappingDefaultCascadeManyValued: TCascadeTypes;
If AutoMapping is enabled, defines the default cascade type for all automapped
associations (AutoMappingDefaultCascade) and
many-valued associations (AutoMappingDefaultCascadeManyValued).
Default values are:
(c) 2016 TMS Software 207
TMS Aurelius Documentation
AutoMappingDefaultCascade := CascadeTypeAll -
[TCascadeType.Remove];
AutoMappingDefaultCascadeManyValued := CascadeTypeAll;
property DefaultStringColWidth: Integer;
Defines the width for string (usually varchar) columns when the width was not particularly specified in
property UseTransactionsInManager: boolean;
Defines the default value for the
TObjectManager.UseTransactions
true, meaning all internal manager operations will be performed with transactions. If you want to disable this (mostly for backward compatibility) for the whole application instead of setting the property for each manager, you can set this property to false.
11.2
Object Factory
In several conditions, Aurelius needs to create entity instances. For example, when
retrieving entities from the database, Aurelius needs to create instances
of those entities. To do that, Aurelius uses an internal object factory. By default, this factory just creates entities by calling a parameter-less constructor named "Create".
Such mechanism works in most cases. But in the case you want to create your entities yourself (for example all your entities have a Create constructor that need to receive a parameter), you can change the object factory and implement it yourself.
To do that, all you need is to implement an IObjectFactory interface (declared in unit Bcl.Rtti.ObjectFactory):
IObjectFactory =
interface
function CreateInstance(AClass: TClass): TObject; end;
It has a single method CreateInstance which receives the TClass and must return a TObject which is a new instance of that class.
Once you have created such instance, you can replace the default one used by Aurelius. You can do it at the
TMappingExplorer level, thus changing the
factory for everything in Aurelius that is related to that explorer:
TMappingExplorer.Default.ObjectFactory := MyObjectFactory; or you can change it for a
TObjectManager object specifically. This gives you
more fine-grained control, for example in case your entities need to be created under a specific context:
Manager.ObjectFactory := MyObjectFactory;
(c) 2016 TMS Software 208
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