Revision as of 12:30, 4 November 2008

Derived Identifiers

JPA 2.0 Root | Enhancement Request

Issue Summary

In JPA 1.0 primary key columns could only be mapped to @Basic attributes. Primary Keys that were derived from Foreign Keys had to be mapped twice, once as the relationship mapping and again as an @Basic. JPA 2.0 adds the functionality to designate a Relationship as providing the primary key for an Entity. Once a relationship is marked as being an ID the PK of that Entity becomes (or includes in the case of composite PK) the ID of the target entity; a derived ID. This feature introduces a new annotation for ID's "MappedByID" used when the derived ID is a component of an EmbeddedID

See JPA 2.0 section 2.1.3.1 for details.

General Solution

Mapping PK to relationship mappings is currently supported in EclipseLink and simple ID's and IdClasses will be easily supported. The EmbeddedID however will be difficult to support as values in the EmbeddedID will need to be populated by EclipseLink on persist(), merge() calls even though they are not the sources of Identity for the Entity. Even more complicated if the derived ID is an IdClass then an instance of that class must be stored in the EmbeddedId which will be new functionality in EclipseLink. Transformation Mapping may be leveraged in combination with the CMP3Policy to support this functionality.

Work Required

1. Develop model for testing

   approx 4 days - should include all permutations of PK combinations. (ie derived IdClass in EmbeddedId)

2. Update Processing

   approx 5 days - processing @Id placement

   approx 4 days - processing @MappedById and support populating EmbeddedIds

   approx 3 days - processing derived IdClass in EmbeddedId

   approx 1 day - processing XML