Need advise for best practice when using Toplink with external transaction

Question

Hello;
Our project is trying to switch from Toplink control transaction to using External transaction so we can make database operation and JMS operation within a single transaction.
Some of our team try out the Toplink support for external transaction and come up with the following initial recommendation.
Since we are not familar with using external transaction, I would like member of this forum and experts, to help comment on whether these recommendation are indeed valid or in line with the best practice. And for folks that have done this in their project, what did you do ?
Any help will be most appreciated.
Data Access Objects must be enhanced to support reading from a TOPLink unit of work when using an external transaction controller. Developers must consider what impact a global transaction will have on the methods in their data access objects (DAOs).
The following findSomeObject method is representative of a “finder” in the current implementation of our DAOs. It is not especially designed to execute in the context of a global transaction, nor read from a unit of work.
public findSomeObject(ILoginUser aUser, Expression queryExpression)
ClientSession clientSession = getClientSession(aUser);
SomeObject obj = null;
try
ReadObjectQuery readObjectQuery = new ReadObjectQuery(SomeObject.class);
readObjectQuery.setSelectionCriteria(queryExpression);
obj = (SomeObject)clientSession.executeQuery(readObjectQuery);
catch (DatabaseException dbe)
// throw an appropriate exception
finally
clientSession.release();
if (obj == null)
// throw an appropriate exception
return obj;
However, after making the following changes (in blue) the findSomeObject method will now read from a unit of work while executing in the context of a global transaction.
public findSomeObject(ILoginUser aUser, Expression queryExpression)
Session session = getClientSession(aUser);
SomeObject obj = null;
try
ReadObjectQuery readObjectQuery = new ReadObjectQuery(SomeObject.class);
readObjectQuery.setSelectionCriteria(queryExpression);
if (TransactionController.getInstance().useExternalTransactionControl())
     session = session.getActiveUnitOfWork();
     readObjectQuery.conformResultsInUnitOfWork(); }
obj = (SomeObject)session.executeQuery(readObjectQuery);
catch (DatabaseException dbe)
// throw an appropriate exception
finally
if (TransactionController.getInstance().notUseExternalTransactionControl())
     session.release();
if (obj == null)
// throw an appropriate exception
return obj;
When getting the TOPLink client session and reading from the unit of work in the context of a global transaction, new objects need to be cached.
public getUnitOfWork(ILoginUser aUser)
throws DataAccessException
     ClientSession clientSession = getClientSession(aUser);
     UnitOfWork uow = null;
     if (TransactionController.getInstance().useExternalTransactionControl())
          uow = clientSession.getActiveUnitOfWork();
          uow.setShouldNewObjectsBeCached(true);     }
     else
          uow = clientSession.acquireUnitOfWork();
     return uow;
}

Answer 1

As it generally is with this sort of question there is no exact answer.
The only required update when working with an External Transaction is that getActiveUnitOfWork() is called instead of acquireUnitOfWork() other than that the semantics of the calls and when you use a UnitOfWork is still dependant on the requirements of your application. For instance I noticed that originally the findSomeObject method did not perform a transactional read (no UnitOfWork). Has the requirements for this method changed? If they have not then there is still no need to perform a transactional read, and the method would not need to change.
As for the requirement that new object be cached this is only required if you are not conforming the transactional queries and adds a slight performance boost for find by primary key queries. In order to use this however, objects must be assigned primary keys by the application before they are registered in the UnitOfWork.
--Gordon