misleading error message if get_or_create not provided with defaults

I had a similar problem with get_or_create that took most of today to find (I'm a Django newbie). Seems as if get_or_create throws DoesNotExist? errors if you get database problems creating too. I had a Foreign key contraint that failed, but that error was somehow hidden by get_or_create. Really annoying! (Tip to anyone experiencing something similar: don't use get_or_create, use the two methods separately instead).

specifically in django.db.models.query, line 228

if a value passed in defaults to get_or_create would cause a null constraint violation, handled like this:

except IntegrityError, e:

return self.get(**kwargs), False

guaranteed to reraise a DoesNotExist?, which is not helpful in the context of get_or_create

Yeah, this is horridly annoying. At some point, staring at the screen, I actually began to think that my Python interpreter was messed up. It seemed to not be catching an exception that it explicitly says to catch.

Anyhow, here's the patch to make some sense.

Integrity!

I've tested this out at the DC Sprint and it seems to be working like a charm. Much nicer error message!

Better just to catch the generic DoesNotExist error right the end (saves a couple of variable resolutions) and there's no need to capture e2 (it's never used). They can be fixed at checkin. Other than that, this is fine and does make things clearer.

On second thoughts, this should have tests so that we don't inadvertently break it again in the future.

(In [8398]) Fixed #6970 -- Raise the original IntegrityError when all required fields aren't specified in get_or_create instead of a misleading DoesNotExist error, thanks deadwisdom.