A
Object Model Requirements

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

This section summarizes OracleAS TopLink's object model requirements. Unlike other products, OracleAS 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 employing 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 the type ValueHolderInterface rather than the original attribute type. The value holder does not instantiate a referenced object until it is needed.

In Java 2, OracleAS 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, OracleAS TopLink uses and requires default (zero argument) constructors to create objects from the database. It is also possible to instruct OracleAS TopLink to use a different constructor, static method, or factory. Refer to "Working with Instantiation Policy" for more information.

Remote Session Requirements

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