Working with Multiple Tables

Descriptors can use multiple tables in mappings. Use multiple tables when:

A subclass is involved in inheritance, and its superclass is mapped to one table while the subclass has additional attributes that are mapped to a second table
A class is not involved in inheritance and its data is spread out across multiple tables

When a descriptor has multiple tables, you must be able to join a row from the primary table to all the additional tables. By default, TopLink assumes that the primary key of the first, or primary, table is included in the additional tables, thereby joining the tables.

TopLink also supports custom methods for joining tables.