#18748: Remove dupe-avoidance logic from the ORM
-------------------------------------+-------------------------------------
Reporter: akaariai | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: master
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Ready for
Severity: Normal | checkin
Keywords: | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by akaariai):
OK, I now know what exclude was used for - when combining queries and the
rhs query has two joins for the same connection we must exclude the alias
used for the first connection. As an example:
{{{
q1 = qs.filter(m2m__f=1)
q2 = qs.filter(m2m__f=1).filter(m2m__f=2)
}}}
Now, we have two joins for m2m in q2, and specifically they have the same
connections for the m2m joins. If we do (q1|q2), then we will reuse all
joins for the first m2m join. If we don't exclude the alias used for the
first m2m join, then we will again reuse the same join for the second m2m
join. This would result in having just one join in the combined query.
This is wrong, as the original rhs query had two joins.
I have done a fix for this in the
https://github.com/akaariai/django/compare/dupe_away, specifically in
https://github.com/akaariai/django/commit/da96154a72c4c4ca53cce198a82bb6af3f87ff64
- note that the exclude arg is still gone, instead I use the reuse arg
here.
I also reworked the .join() implementation
(https://github.com/akaariai/django/commit/b42280f45c7cd0fcde835ee4665e9d67327fda1d).
I feel the code is much improved, but I can't claim to understand the
existing code in full. I am afraid that there are other regressions
lurking...
If anybody can review this I would much appreciate it!
--
Ticket URL: <https://code.djangoproject.com/ticket/18748#comment:8>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To post to this group, send email to django-updates@googlegroups.com.
To unsubscribe from this group, send email to
django-updates+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
