Status: New
Owner: ----
New issue 604 by [email protected]: Persist: Automatically starting a
UnitOfWork in JpaPersistService.get()
http://code.google.com/p/google-guice/issues/detail?id=604
JpaPersistService.get() starts a UnitOfWork if one has not already been
started. It then does a checkState to ensure that a UnitOfWork has been
started, with a message indicating that the user should ensure that they
start a UnitOfWork before trying to get() an EntityManager. Since a
UnitOfWork is always started before this check, it'll never throw an
exception.
However, I think that the correct behavior here would be to throw the
exception rather than starting a UnitOfWork for the user. The problem is
that an EntityManager will be set in the ThreadLocal, but it probably will
not be removed because if the user didn't call UnitOfWork.begin() before
getting the EntityManager, they probably won't call UnitOfWork.end() after
either. This seems like a problem to me.
Is the point to allow users to choose to not manually start a UnitOfWork
and have it only start when (and if) it's needed? And then to have them
call end() at some point in case one was started? I can see the advantage
in that, but I still somewhat worry that it makes it too easy to leave an
unclosed EntityManager in the ThreadLocal. I also think in many cases, the
EntityManager would likely be retrieved even if it weren't used, either due
to a high level @Transactional method or due to a class that has the
EntityManager injected into it being instantiated.
I think my preference would be to require that either a UnitOfWork be
manually started before a class that has an EntityManager injected into it
is instantiated (already the case for any webapp using PersistFilter) or
that a Provider<EntityManager> be injected and called in each transactional
method when a UnitOfWork is guaranteed to be active.
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