[hibernate-dev] Overriding JpaMergeEventListener with JpaEntityCopyAllowedMergeEventListener

[Gail Badner]

CC'ing hibernate-dev...

----- Original Message -----
> From: "Gail Badner" <gbadner at redhat.com>
> To: "Steve Ebersole" <steve at hibernate.org>, "Emmanuel Bernard" <emmanuel at hibernate.org>
> Sent: Friday, June 20, 2014 4:25:56 PM
> Subject: Overriding JpaMergeEventListener with JpaEntityCopyAllowedMergeEventListener
> 
> I am trying into figure out how to override JpaMergeEventListener with
> JpaEntityCopyAllowedMergeEventListener as described in [1]. This
> documentation does not describe how to deal with injecting CallbackRegistry
> into an overridden MergeEventListener.
> 
> CallbackRegistry is an SPI, but JpaMergeEventListener and
> CallbackRegistryConsumer are internal.
> JpaEntityCopyAllowedMergeEventListener is also internal.
> 
> I was planning to document MyIntegrator.integrate(..) for enabling entity
> copies, but I don't like the idea of documenting an internal event listener
> for that functionality.
> 
> Here is one alternative that minimizes exposing private classes/methods:
> 
> public class MyIntegrator implements org.hibernate.integrator.spi.Integrator
> {
> 
>     public void integrate(
>             Configuration configuration,
>             SessionFactoryImplementor sessionFactory,
>             SessionFactoryServiceRegistry serviceRegistry) {
>         final EventListenerRegistry eventListenerRegistry =
>         serviceRegistry.getService( EventListenerRegistry.class );
>         final MergeEventListener mergeEventListener =
>         mergeEventListenerGroup.listeners().iterator().next();
>         final JpaEntityCopyAllowedMergeEventListener
>         entityCopyAllowedMergeEventListener =
>                 new JpaEntityCopyAllowedMergeEventListener();
>         entityCopyAllowedMergeEventListener.initializeFrom(
>         mergeEventListener );
>         registry.setListeners( EventType.MERGE,
>         entityCopyAllowedMergeEventListener );
>      }
>     ...
> }
> 
> public class JpaEntityCopyAllowedMergeEventListener extends
> JpaMergeEventListener {
>     ...
>     public void initializeFrom(MergeEventListener mergeEventListener) {
>         if ( JpaMergeEventListener.class.isInstance( mergeEventListener ) ) {
>             injectCallbackRegistryFrom( (JpaMergeEventListener)
>             mergeEventListener );
>         }
>     }
>     ...
> }
> 
> public class JpaMergeEventListener extends DefaultMergeEventListener
> implements CallbackRegistryConsumer {
>     ...
>     protected void injectCallbackRegistryFrom(JpaMergeEventListener
>     jpaMergeEventListener) {
>         injectCallbackRegistry( jpaMergeEventListener.callbackRegistry );
>     }
>     ...
> }
> 
> Another alternative is to change JpaEntityCopyAllowedMergeEventListener to be
> a Proxy that holds an instance of the original JpaMergeEventListener.
> Everything except for createEntityCopyObserver() could be delegated to the
> stored JpaMergeEventListener. There would be no need to call
> injectCallbackRegistry(CallBackRegistry).
> 
> It might be possible to have one Proxy for
> JpaEntityCopyAllowedMergeEventListener and
> EntityCopyAllowedMergeEventListener holding an instance of
> MergeEventListener, but that Proxy wouldn't implement
> CallbackRegistryConsumer or HibernateEntityManagerEventListener. Does that
> matter for an overridden event listener if the CallbackRegistry does not
> have to be injected?
> 
> Is there some other way of doing this that I've missed?
> 
> Thanks,
> Gail
> 
> [1]
> http://docs.jboss.org/hibernate/orm/4.3/devguide/en-US/html/ch07.html#registering-listeners-example
> 
>