NullableAttribute Class
Allows a table column mapped to an entity class‘s field/property storing NULL values.
Declaration
NullableAttribute = class(
TCustomAttribute
)Remarks
All columns are set to contain only non-NULL values, except for the following:
Columns mapped to nullable fields or properties;
Columns storing BLOB values (mapped to TBytes or TStrings fields/properties, or fields/properties marked with the BlobAttribute);
Columns that correspond to foreign keys created by any of the following: entity references used in relationships, inherited primary keys in tables created for TdxMapInheritanceType.OwnTable descendant classes, etc.;
Columns that correspond to fields/properties mapped from TdxMapInheritanceType.ParentTable descendant classes to their ancestor’s table.
Applying the NullableAttribute to a specific column overrides the default behavior and allows it to store NULL values. This is useful, for instance, when binding entity objects to data-aware controls using the TdxEMFDataSet component, because these controls normally populate a newly inserted table record with NULL values.