Working with a Wrapper Policy

TopLink allows you to use wrappers (or proxies) in cases where the persistent class is not the same class that is to be presented to users.

For example, in the Enterprise JavaBeans specification, the Entity bean class (the class that implements javax.ejb.EntityBean) is persistent but is hidden from users who interact with a class that implements javax.ejb.EJBObject (the remote interface class). In this example, the EJBObject acts as a proxy or wrapper for the EntityBean.

In cases where such a wrapper is used, TopLink continues to make the class specified in the descriptor persistent, but returns the appropriate instance of the wrapper whenever a persistent object is requested.

Use a wrapper policy to tell TopLink how to create wrappers for a particular persistent class, and how to obtain the underlying persistent object from a given wrapper instance.

If you specify a wrapper policy, TopLink uses the policy to wrap and unwrap persistent objects as required:

Wrapper policies implement the interface oracle.toplink.descriptors.WrapperPolicy.
A wrapper policy is specified by setting the wrapper policy for the TopLink descriptor.
By default, no wrapper policy is used (the wrapper policy for a descriptor is null by default).
Wrapper policies cannot be set using the TopLink Mapping editor and can only be set using Java code.
Note: Wrapper policies are advanced options. Using a wrapper policy may not be compatible with other TopLink features.