Flushing EntityManger but database record is not written.

[swenvogel]

Hi,

i have a question about manually flushing the entity manager.
In the following test code snippet i persist a DispatchOrder
object and afterwards directly call flush.

The problem is that the new record is not written to the
database until the method end. Because of that the status
updates in the loop are also not visible until the method ends.

In my use case i have a long running process and users should
be able to query the process status through the informations
in the database. But this problem users can only the result
not the progress.

Any ideas how to do this?

@Name("dispatchProcess")
@Scope(ScopeType.SESSION)
public class DispatchProcess {

  @In
  private EntityManager entityManager;

  private DispatchOrder order;

  public void start() {
    order.setStatus(DispatchStatus.InProgress);
          
    Session session = (Session) entityManager.getDelegate();
    session.setFlushMode(FlushMode.MANUAL);
          
    entityManager.persist(order);
    entityManager.flush();

    for (long i = 0; i < 3; ++i) {
         order.getFinishedRecipients().add(i);

         Thread.sleep(3000);
         entityManager.flush();
    }
    
    order.setStatus(DispatchStatus.Finished);
  }


  public void setOrder(DispatchOrder order) {
    this.order = order;
  }        

}

[raimundhoelle]

No, the changes will be written to the database - have you inspect the hibernate logging? (Maybe you have to enable it in your persistence.xml)

But the changes won't be visible to other sessions until they are committed - normally automatically at end of the event (after leaving your method).

So you have either to bypass the transaction handling and do it by yourself (using SEAM's user transactions) or use another approach to signal the progress to other sessions, e. g. SEAM events.

Ich think the latter would be a very better method because it avoids polling on database tables which may kill your database performance in a multi user environment.

Regards, Raimund

[swenvogel]

Thanks for your response.

I think i will handle the transaction handling by myself. I also have found
this great thread:

http://seamframework.org/Community/UserDefinedTransactionsWithSeamPOJOComponentExample