#10790: Too many joins in a comparison for NULL.
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Reporter: mtredinnick | Owner:
Type: Bug | mtredinnick
Component: Database layer | Status: new
(models, ORM) | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by famousactress@…):
Yeah, I'm almost done cleaning up the unit tests and commenting each of
them, because I think they provide a pretty thorough set of cases that
will be helpful with whatever solution we eventually arrive at. I'm also
rewording the comment language in the tests to not talk about which joins
should be trimmed, etc.. but rather just what we're testing and how the
queries are expected to work. I'm also seeing at least one inconsistency
with the way queries are produced that I don't think was introduced by
this patch (will confirm), so I'll probably end up spinning out a separate
ticket for that bit after confirming on the mailing list it's not intended
behavior.
As for the patch itself, my limited understanding of how things are
working matches yours. The demoted join stuff feels like a really strange
way to go about this. It makes loads more sense to me to detect these
conditions and treat them as simple field comparisons.. ie: don't create
the joins in the first place.
Regardless, I think this ticket is really important to work on. The
.exclude() hack works okay for simple cases pre-1.4, but most Django code
I come across doesn't use it.. most people don't know about this bug, or
the exclude() workaround... In 1.4 a lot of data access code gets a lot
worse/slower. The patch, if severely imperfect, at least provides some
evidence that we can do way better.
--
Ticket URL: <https://code.djangoproject.com/ticket/10790#comment:32>
Django <https://code.djangoproject.com/>
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