In the framework, I'm trying to enforce optimistic locking and a unique
constraint on the "name" attribute. For optimistic locking, there's not a lot
I can do except kick them out (they can always open a new window and use their
back button to copy their changes and merge them in). For name conflicts, I
thought to add a message and let them try something else.
Here's the code:
| @End @Transactional @Override
| public String update() {
| getInstance().setUpdatedOn(new Date());
| try {
| return super.update();
| } catch (OptimisticLockException e) {
| facesMessages.add("#{messages.staleEditRule}");
| return "aborted";
| } catch (EntityExistsException e) {
| facesMessages.add("name", "#{messages.errNameExists}");
| return null;
| } catch (RuntimeException e) {
| facesMessages.add(e.toString());
| return null;
| }
| }
|
Only problem is, this appears to work -- you correct the name, hit update, your
changes appear to take, you're back in the view screen -- but when you next
view the entity you edited, you find your changes never actually took.
I think I understand why this is happening -- the session is no longer valid
after an exception -- but there's no indication even in log messages that this
has happened, and the update was just silently dropped.
So I have two questions:
1) Is the lost update detectable somehow? I feel like EntityManager should
have screamed at me for trying to update again after the exception, but it gave
nary a peep.
2) How do I gracefully recover from errors on update and reset the
entityManager so further updates can succeed? Should I make the unique
constraint a validator instead? Enforcing unique constraints must be a FAQ for
Hibernate, but I haven't found an answer yet.
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