JPA @GeneratedValue始终为null

Question

I'm using MySQL / JPA, and the auto-generated IDs on persisted entities are not becoming available even after commit. Here's the code where it happens:

synchronized (em.getTransaction()) {
    while (em.getTransaction().isActive()) {
        em.getTransaction().wait();
    }
    em.getTransaction().begin();
    try {
        em.merge(transmissor);
        em.merge(poco);
        em.flush();
        //em.refresh(poco);           
        System.out.println("ID: " + poco.getIdEstacao());
    } catch (Exception ex) {
        System.out.println(ex.toString());
        ex.printStackTrace();
    }
    // Some other unrelated code...
    em.getTransaction.commit();
    em.getTransaction.notify();
    System.out.println("ID: " + poco.getIdEstacao());
}

Both after em.flush() and after em.getTransaction.commit() , poco.getIdEstacao returns null . And if I try to em.refresh(poco) it throws an exception:

java.lang.IllegalArgumentException: Can not refresh not managed object:unesp.lebac.aquitel.dataLink.enitity.Poco[ idEstacao=null ].

Any ideas why this happens? Thanks in advance!

Answer 1

EntityManager.merge() doesn't modify the object passed as argument, and doesn't make it managed. It copies the state of the object passed as argument to a managed entity instance, and returns this managed entity instance. So if you want to get the managed entity, you need

poco = em.merge(poco);