Monday, December 30, 2013

Re: Open Session In View not working (locator?)

On Monday, December 30, 2013 8:17:07 PM UTC+1, Yan wrote:
Hi there, 

I am integrating GWT 2.5.1 with Spring 3.0 backend.  Run into a problem that OSIVP should fix but it is not. 

A parent object contains a list of children objects, both are EntityProxy. On client side, I update the child proxy and my Server side API simply saves the parent.  On the server side, my updates to the child object disappears by the time server business logic is invoked.  My transaction starts and commits in business service layer. I have already used one single entity manager instance per request by using ThreadLocal.

Without using OSIVP, I did observe if I explicitly start a transaction in my request factory servlet when request comes in, and then commit the transaction in the servlet at the end, the problem is fixed. Therefore, I have to group everything under the same transaction (inside servlet, rather than in service layer), in addition to use one single entity manager pre request, is that correct?

No. Transactions really should be scoped to the service methods at most.
Everyone said that the fix is to use OSIVP, however, I do not see it is fixing the problem afterwards. For whatever reason, using OSIVP does not have the same effect. 

1) In my EntityLocator class, how do I get entityManager?   Some has posted this code, this is what I used. But, does not it start a new entity manager rather than using what is attached to the thread?

private void init() {
        HttpServletRequest request = RequestFactoryServlet.getThreadLocalRequest();
        ApplicationContext context = WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext());
        EntityManagerFactory entityManagerFactory = context.getBean(EntityManagerFactory.class);
        entityManager = entityManagerFactory.createEntityManager();
        // then cache this entityManager in locator instance

You should call createEntityManager in a servlet filter prior to the RequestFactoryServlet, or call it in some helper class if you want it initialized lazily.
And you could store that EntityManager in the request's attributes rather than a ThreadLocal (but a ThreadLocal will work too).

That said, I don't know Spring, so there might be other ways to get at the EntityManager than calling createEntityManager and "caching" its result yourself.
Possibly something like ((EntityManagerHolder) TransactionSynchronizationManager.getResource(emf)).getEntityManager(), where "emf" is your singleton EntityManagerFactory.

This code is most likely why your app doesn't work: you're not actually using OSIV.
2) In my DAO class, do I need to declare my entity manager as extended like this?  That is what I did. 

private EntityManager em;

I suppose so (I don't know Spring or JPA much)
3) How does Spring OpenEntityManagerInViewFilter start a transaction?

It doesn't, fortunately. 

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