On Aug 24, 2006, at 10:41 AM, David Jencks wrote:
I've been looking at the ejb 3 persistence spec and it looks to me
as if there are some poorly explained bits. Anyone have any clues
about these or any clue about where I could get an answer?
1. The @PersistenceContext annotation appears to be per jee
component (web app or ejb). You can specify a map of properties to
pass in to the EMF.createPersistenceContext method. Lets suppose
you have tx scoped PC, and you have 2 ejbs with tx Required and one
calls the other, and one specifies a map of properties and the
other doesn't (or they specify different maps). What's supposed to
happen?
s/EMF.createPersistenceContext/EMF.createEntityManager/
I don't think it ever was established that the container had to
consider and evaluate vendor specific data while determining if two
entity managers are equivalent. It's vendor specific data, you have
no logical way to evaluate it. You can do a string equals, but it's
not your data and you don't actually know if that's significant.
2. What's supposed to happen when you try to use a CM tx scoped EM
outside a JTA tx? Section 5.6.1 seems to imply we aren't supposed
to just throw an exception, but section 5.9.1 seems to imply there
is no provider EM in back of the CM EM to do any work without a JTA
tx. Are we supposed to create and close a provider EM for each
call outside a tx?
You can call read-only operations on the EntityManager with no tx and
no exceptions thrown, you just can't call the write methods persist,
merge, remove, and refresh.
I'm sure I'll have more questions later.... I have one more non-
spec question which perhaps I need to ask the openjpa guys...
- How heavyweight are EntityManagers? Is it more efficient to
create a new one or pool them? Are they cheap enough so every CM
tx-scoped EM can have a "outside tx" provider EM attached to it in
case anyone is dumb enough to do work outside a tx? Is this more
or less resource efficient than creating a new EM for each out-of-
tx use?
That I don't know.
-David
thanks
david jencks
