Configuring Instantiation Policy

The TopLink runtime instantiates new instances of a class according to the instantiation policy you configure on the class's descriptor.

Table 28-31 summarizes which descriptors support an instantiation policy.

Table 28-31 Descriptor Support for Instantiation Policy

Descriptor	Using TopLink Workbench	Using Java
Relational Descriptors
Object-Relational Descriptors
EIS Descriptors
XML Descriptors

You can specify one of the following types of instantiation policy:

• Default: TopLink creates a new instance of a class by calling the class's default constructor.

• Method: TopLink creates a new instance of a class by calling a public static method that you define on the class descriptor.

• Factory: TopLink creates a new instance of a class by calling the appropriate methods on a separate class that you implement according to the Factory design pattern.

Using TopLink Workbench

To set the instantiation policy for a descriptor, use this procedure:

1. In the Navigator, select a descriptor.

   If the Instantiation advanced property is not visible for the descriptor, right-click the descriptor and choose Select Advanced Properties > Instantiation from the context menu or from the Selected menu.

2. Click the Instantiation tab.

   Figure 28-40 Instantiation Tab

   
   

Use the following information to enter data in each field on the tab:

Field	Description
Use Default Constructor	Specify if the default constructor of the class instantiates a new instance.
Use Method	Specify a method to execute to create objects from the database.
Method	Select the name of a method to be executed to create objects from the database. The method must be a public, static method on the descriptor's class and must return a new instance of the object.
Use Factory	Specify an object factory method.
Factory Class	Select the class of the factory object that creates the new instances.
Factory Method	Select the method to be used to obtain a factory object. Choose <nothing> to use the default constructor.
Instantiation Method	Select the method to be called on the factory object to obtain a new instance that will be populated with data from the data source.

Using Java

Use one of the following ClassDescriptor methods to set the appropriate type of instantiation policy:

• useDefaultConstructorInstantiationPolicy

• useMethodInstantiationPolicy

• useFactoryInstantiationPolicy