Module eclipselink

Package org.eclipse.persistence.annotations

Annotation Interface ClassExtractor

@Target(TYPE)
@Retention(RUNTIME)
public @interface ClassExtractor

A ClassExtractor allows for a user defined class indicator in place of providing a discriminator column. The class has the following restrictions:

• It must extend the ClassExtractor class and implement the ClassExtractor.extractClassFromRow(org.eclipse.persistence.sessions.DataRecord, org.eclipse.persistence.sessions.Session) method.
• That method must take a database row (a DataRecord/Map) as an argument and must return the class to use for that row.

This method will be used to decide which class to instantiate when reading from the database. It is the application's responsibility to populate any typing information in the database required to determine the class from the row.

The ClassExtractor must only be set on the root of an entity class or sub-hierarchy in which a different inheritance strategy is applied. The ClassExtractor can only be used with the InheritanceType.SINGLE_TABLE and InheritanceType.JOINED inheritance strategies.

If a ClassExtractor is used then a DiscriminatorColumn cannot be used. A DiscriminatorColumn also cannot be used on either the root or its subclasses.

In addition, for more complex configurations using a ClassExtractor and an InheritanceType.SINGLE_TABLE strategy, the descriptor's withAllSubclasses and onlyInstances expressions should be set through the ClassExtractor's initialize method.

See Also:

• ClassExtractor
• InheritancePolicy.setWithAllSubclassesExpression(org.eclipse.persistence.expressions.Expression)
• InheritancePolicy.setOnlyInstancesExpression(org.eclipse.persistence.expressions.Expression)

Author:

Guy Pelletier

Required Element Summary

Required Elements

Modifier and Type	Required Element	Description
Class<?>	value	Defines the name of the class extractor that should be applied to this entity's descriptor.

Element Details

value

Class<?> value

Defines the name of the class extractor that should be applied to this entity's descriptor.