Built-in Attributes

• Dec 28, 2020
• 3 minutes to read

The ExpressEntityMapping Framework uses built-in attributes and runtime type information (RTTI) to map entities defined in an entity model to data store objects. These attributes allow you to provide mapping details, establish relationships between entity classes, define entity inheritance, etc. Add the dxEMF.Attributes unit to the ‘uses’ clause to enable these attributes in your project.

The following table lists all built-in attributes by mapping category.

Mapping Category	Attribute	Description
Entity (applies to classes)	Entity	Marks a class as an entity class.
Table and Column (Simplified Mapping) (applies to classes and fields/properties)	Automapping	Enables simplified table and column mapping for an entity class.
	NonPersistent	Excludes a field from a schema created for an entity class marked with the Automapping attribute.
Table (applies to classes)	Table	Specifies a data store table to which an entity class maps its data.
	SchemaName	Specifies the name of a database schema in which a table mapped to an entity class is created.
Inheritance (applies to classes)	Inheritance	Specifies where an entity descendant class stores its data.
	DiscriminatorColumn	Specifies a discriminator column whose values identify rows that correspond to an entity class and its descendants in the class’s mapped table.
	Discriminator	Specifies a discriminator column value that uniquely identifies rows that correspond to an entity class in the ancestor’s table.
Primary Key Column (applies to fields/properties)	Key	Specifies one or more table columns that make up a primary key for an entity class.
	Generator	Specifies how an auto-incremented primary key generates its values.
Column (applies to fields/properties)	Column	Specifies a table column to which an entity class maps its field/property.
	DBType	Specifies the data store type of a table column to which an entity class’s field/property maps its data.
	Nullable	Allows a table column mapped to an entity class’s field/property storing NULL values.
	Default	Reserved for future use.
	Size	Specifies the size of a column to which a string or BLOB data field/property of an entity class is mapped.
	Blob	Indicates if a column to which a string or BLOB data field/property of an entity class is mapped stores Memo or BLOB data.
	ReadOnly	Makes a TdxEMFDataSet component’s field bound to an entity class’s field/property read-only.
Column Index (applies to classes)	Indexes	Specifies one or more columns that make up a non-unique index on a data store table to which an entity class is mapped.
Column Index (applies to fields/properties)	Indexed	Specifies if a field’s/property’s mapped column makes up a non-unique index on a data store table to which an entity class is mapped.
	Unique	Creates a unique index on a table column that is mapped to an entity class’s field/property.
Relationship (applies to fields/properties)	Association	Identifies the end of an association that establishes a one-to-many entity relationship.
	Aggregated	Indicates if an entity class’s collection field/property referencing an association‘s “many” end aggregates its referenced entity objects.
	NoForeignKey	Disables automatic creation of foreign key constraints for an association.

Refer to the descriptions of the attribute classes listed above for details and code examples on how to use them.