How can I get optimistic concurrency with JPA annotation - optimistic-locking

Question

I am using JPA 3, with annotation (no mapping file) and with provider org.hibernate.ejb.HibernatePersistence
I need to have optimistic concurrency.
1)I tried to rely on the tag called , it did not work.
2)
So I decided to do it with java code. I have a mergeServiceRequest method and an object with type Request as follows: I start a transaction, lock the request object,
then try to get a Request object newRequest from database, compare its timestamp with the current one request. If they do not match, I throw an exception; if they match, then I update the current request enter code herewith current time and save it to database.
I need to lock the object manually, because by starting a transaction from session, it does not put a lock on the row in database. I wrote some java code which shows that a transaction does not lock the record in database automatically.
Problem with this approach is the query
Request newRequest=entityManager.createQuery("select r from Request r where serviceRequestId = " + request.getServiceRequestId());
always return same object as request. "request" is in the session entityManger, and the query always return what is cached in the session. I tried all the five query.setHint lines and I still get same result: no database query is performed, the result is from session cache directly.
#Transactional
public void mergeServiceRequest(Request request) {
System.out.println("ServiceRequestDao.java line 209");
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
entityManager.lock(request, LockModeType.WRITE); // use to lock the database row
Query query = entityManager.createQuery("select r from Request r where serviceRequestId = " + request.getServiceRequestId());
//query.setHint("javax.persistence.cache.retrieveMode", "BYPASS");
//query.setHint("org.hibernate.cacheMode", CacheMode.REFRESH);
//query.setHint("javax.persistence.cache.retrieveMode", CacheMode.REFRESH);
//query.setHint("javax.persistence.retrieveMode", CacheMode.REFRESH);
//query.setHint(QueryHints.CACHE_USAGE, CacheUsage.DoNotCheckCache);
Request newRequest=(Request)query.getSingleResult();
if (! newRequest.getLastUpdatedOn().equals(request.getLastUpdatedOn())) {
throw new StaleObjectStateException(request.getClass().toString(), request.getServiceRequestId());
}
request.setLastUpdatedOn(new Date(System.currentTimeMillis()));
entityManager.persist(request);
entityManager.flush();
transaction.commit();
}
3)So I also tried to use another session get query the newRequest, if I do that, the newRequest will be different from request. But for some reason, if I do that, then the lock on request object is never released, even after the transaction commit. Code looks like below
#Transactional
public void mergeServiceRequest(Request request) {
System.out.println("ServiceRequestDao.java line 209");
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
entityManager.lock(request, LockModeType.WRITE); // use to lock the database row
Request newRequest=findRequest(request.getServiceRequestId()); // get it from another session
if (! newRequest.getLastUpdatedOn().equals(request.getLastUpdatedOn())) {
throw new StaleObjectStateException(request.getClass().toString(), request.getServiceRequestId());
}
request.setLastUpdatedOn(new Date(System.currentTimeMillis()));
entityManager.persist(request);
entityManager.flush();
transaction.commit();
//lock on the database record is not released after this, and even after entityManager is closed
}
Could anyone help me on this?
Thanks.
Daniel