Provides callbacks from the Session to the persistent object. Persistent classes may implement this interface but they are not required to.

onSave: called just before the object is saved
onUpdate: called just before an object is updated, ie. when Session.update() is called
onDelete: called just before an object is deleted
onLoad: called just after an object is loaded

onLoad() may be used to initialize transient properties of the object from its persistent state. It may not be used to load dependent objects since the Session interface may not be invoked from inside this method.

A further intended usage of onLoad(), onSave() and onUpdate() is to store a reference to the Session for later use.

If onSave(), onUpdate() or onDelete() return VETO, the operation is silently vetoed. If a CallbackException is thrown, the operation is vetoed and the exception is passed back to the application.

Note that onSave() is called after an identifier is assigned to the object, except when identity column key generation is used.