Detached Object?

[Chadwick Baatz <cb...@us.ibm.com>]

I'm new to using JPA, so I might be misinterpreting how the detached object
concept should work.  The problem I am having is integrating JPA into a
service  based system.  I have an entity A that I would like to share
between many different entities (B).  There will be time when more than one
request arrives where different entity B's will redefine A.  So the
instance of A are not "detached" but rather new duplicates of a unique
entity.  I can catch duplicate entities by looking them up based on a
unique key, but when I try to merge that object the entity manager
attempts to insert the new value.  This is true even though there is a
defined set of unique columns and I've set the identity value.  Should I
get the persisted entity then manually update the fields?  It seems to me
that the merge command should be able to handle this.

DAO Code:
  public A saveEntity(A entity)
  {
    EntityTransaction transaction = this.manager.getTransaction();
    transaction.begin();

    // Determine if the injection is new or a duplicate
    if(entity.getId() <= 0)
    {
      Query query = this.manager.createNamedQuery("findByUNK");
      query.setParameter("field", entity.getField());
      query.setParameter("className", entity.getClassName());
      query.setParameter("url", entity.getUrl());
      query.setParameter("injectionType", entity.getInjectionType());

      List entities = query.getResultList();

      A persistedEntity = (A)(entities != null && entities.size() > 0 ?
entities.get(0) : entity);
      entity = persistedEntity ;
    }

    if(entity .getId() > 0 || this.manager.contains(entity ))
    {
      entity = this.manager.merge(entity );
    }
    else
    {
      this.manager.persist(entity );
    }

    transaction.commit();

    return entity ;
  }