A
Object Model Requirements

Oracle9iAS TopLink requires that classes must meet certain minimum requirements before they can become persistent. TopLink also provides alternatives to most requirements. TopLink uses a non-intrusive approach using a meta-data architecture that allows for almost no object model intrusions.

This section summarizes TopLink's object model requirements. Unlike other products, TopLink does not require any of the following:

• Persistent superclass or implementation of persistent interfaces

• Stored, delete or load methods required in the object model

• Special persistence methods

• Generating source code into or wrapping the object model

Persistent Class Requirements

The attribute requirements vary, depending on your Java version. When using Java 2, you can use direct access on private or protected attributes. Refer to Chapter 4, "Understanding Descriptors" for more information on direct and method access.

When using non-transparent indirection, the attributes must be of type ValueHolderInterface rather than the original attribute type. The value holder does not instantiate a referenced object until it is needed.

In Java 2, TopLink provides transparent indirection for Collection and List attribute types for any collection mappings. Using transparent indirection does not require the usage of ValueHolderInterface, or any other object model requirements.

Refer to Chapter 6, "Understanding Relationship Mappings" for more information on indirection and transparent indirection.

Constructor Requirements

By default, TopLink uses and requires default (zero argument) constructors to create objects from the database. It is also possible to instruct TopLink to use a different constructor, static method, or factory. Refer to "Working with Instantiation Policy" for more information.

Remote Session Requirements

If the TopLink Remote Session is used, all persistent classes to be used remotely must implement the Serializable interface.