[jboss-jira] [JBoss JIRA] Created: (JBCACHE-835) PojoCache need merge api?

[Ben Wang (JIRA)]

PojoCache need merge api?
-------------------------

                 Key: JBCACHE-835
                 URL: http://jira.jboss.com/jira/browse/JBCACHE-835
             Project: JBoss Cache
          Issue Type: Feature Request
      Security Level: Public (Everyone can see)
          Components: PojoCache
            Reporter: Ben Wang
         Assigned To: Ben Wang
             Fix For: PojoCache


Currently, PojoCache attach api will override the current pojo in the cache. It doesn't really have a merge functionality. Question is do we really need to have a merge api?

The following is the spec for the ejb3 entity manager merge api. However, the ejb3 em api doesn't quite apply in the case of PojoCache. You can see the object identity is by PK instead of reference. So during merge, a copy of Pojo is created instead.

The TravelAgentBean.updateCabin() method takes its cabin parameter and merges it back into the current persistence context of the entity manager by calling the merge() operation:  
@PersistenceContext EntityManager entityManager;

@TransactionAttribute(REQUIRED)
public void updateCabin(Cabin cabin) {
   Cabin copy = entityManager.merge(cabin);
}
The changes made by the remote Swing client will now be reflected in persistence storage when the entity manager decides to flush to the database. The following rules apply when merging in the cabin parameter of the updateCabin() method:
•	If the entity manager isn't already managing a Cabin instance with the same ID, a full copy of the parameter is made and returned from the merge() method. This copy is managed by the entity manager, and any additional setter methods called on this copy will be synchronized with the database when the EntityManager decides to flush. The cabin parameter remains detached and unmanaged.
•	If the entity manager is already managing a Cabin instance with the same primary key, then the contents of the parameter are copied into this managed object instance. The merge() operation will return this managed instance. The cabin parameter remains detached and unmanaged.



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