the never ending flow of optimistic locking questions

[beligum]

Hi all,

This question must be getting boresome to some of you experts here,
but please help an intermediate developer along with some answers to a few simple questions regarding the subject.

I use the @Version annotation in my EJB3 entity bean (Seam, JTA), and, while a user edits the bean-contents, it's possible the info is updated through a JMS-callback from an external source.

Now, I would like to select a few (modified-behind-the-scenes) fields from the database, and let them precede the user-input whatsoever.

So, when I call my entityManager.flush() method (Seam-managed em), it throws a StaleObjectStateException, because of the JMS-update. In this post (http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3919517#3919517), Gavin points out that it's possible to present the user with the changes made in the DB, by starting up a new context/transaction. He even points out how to do it, but in his own expert-style, the explanation is still quite cryptic to me.

Can anyone elaborate on the:

To "get" a new PC/txn to work with, call a session bean in the context of a REQUIRES_NEW transaction (if it is stateful, it needs to be a newly instantiated SFSB).

This is my relevant code (a conversation-scoped SFSB in a long-running conversation/transaction):

public String updateEntity()
{
 ...
 try {
 entityManager.merge(getSelectedInode());
 entityManager.flush();

 return "success";
 }
 catch (OptimisticLockException e) {
 VersionConflictManager conflictManager = (VersionConflictManager)Component.getInstance("versionConflictManager");
 File dbFile = (File)conflictManager.getConflictingDbObject(File.class, getSelectedInode().getFileSystemEntity().getId());
 System.out.println("test");
 }
}

And here's my VersionConflictManager

@Stateful
@Scope(CONVERSATION)
@Name("versionConflictManager")
public class VersionConflictManager implements Serializable
{

 //-----VARIABLES-----
 @In(create=true)
 EntityManager entityManager;

 //-----CONSTRUCTORS-----
 public VersionConflictManager()
 {
 }

 //-----GETTERS/SETTERS------
 @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
 public Object getConflictingDbObject(Class entityClass, int id)
 {
 return entityManager.find(entityClass, id);
 }

 @Remove
 @Destroy
 public void destroy()
 {
 }
}

Apparently, I'm missing something, because I get a StaleObjectStateException when I try to instantiate the VersionConflictManager in the catch-code.

Any help is appreciated,

bram

PS: I'm cross-posting this from the Persistence,JBoss/CMP, Hibernate, ... forum, to raise my chances in getting a response (http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4055537#4055537), please forgive me my insolence