Defining Inheritance Mapping

Inheritance can be mapped in different ways.

For more information about this type of mapping, see Inheritance transformation.

You can apply those three inheritance mapping strategies or even mix strategies. You should define primary identifier on the entity class that is the root of the entity hierarchy.

Given the following inheritance hierarchy:

We will describe in detail how to define inheritance mapping applying these mapping strategies.

• Applying Table Per Class Hierarchy Strategy
  The whole class hierarchy should be mapped to one table. There should be one discriminator column defined to distinguish instances of difference classes in the hierarchy. The column can have character based type or integer type.
• Applying Joined Subclass Strategy
  Each entity class should be mapped to its own primary table. Each primary table has a reference key referring to a primary table of its parent class except for the primary table of the root class. The reference key should join on the primary key of the primary table.
• Applying Table Per Class Strategy
  Each class should be mapped to its own primary table. All persistent attributes of the class, including inherited persistent attributes, are mapped to columns of the table for the class. Given the following example:

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Created October 7, 2009. Send feedback on this help topic to Sybase Technical Publications: pubs@sybase.com