The optimization introduced in 7acef095d73 did not properly handle
deletion involving filters against aggregate annotations.
It initially was surfaced by a MariaDB test failure but misattributed
to an undocumented change in behavior that resulted in the systemic
generation of poorly performing database queries in 5b83bae031.
Thanks Anton Plotkin for the report.
Refs #23576.
Backport of f6405c0b8ef7aff513b105c1da68407a881a3671 from master
Thanks Adam Johnson for the report.
Regression in 7acef095d73322f45dcceb99afa1a4e50b520479.
Backport of 972000420e08703dd4981466ff67adcd5a61ad4b from master
This required moving the entirety of DELETE SQL generation to the
compiler where it should have been in the first place and implementing
a specialized compiler on MySQL/MariaDB.
The MySQL compiler relies on the "DELETE table FROM table JOIN" syntax
for queries spanning over multiple tables.
Reduced the number of queries required when performing cascade deletion
for a model referenced multiple time by another one by performing an
union of reference lookups.
The non-referenced fields can only be deferred if no deletion signals
receivers are connected for their respective model as connected as these
receivers might expect all fields of the deleted model to be present.
Thanks Ed Morley for the report.
Thanks to Trac alias ppetrid for the report and Tim for the review.
Conflicts:
django/db/models/deletion.py
tests/delete/tests.py
Forward port of 7c3ef19978b36b61db88a519f799f1ce8d019679 from stable/1.8.x
Field.rel is now deprecated. Rel objects have now also remote_field
attribute. This means that self == self.remote_field.remote_field.
In addition, made the Rel objects a bit more like Field objects. Still,
marked ManyToManyFields as null=True.
SQLite doesn't work with more than 1000 parameters in a single query.
The deletion code could generate queries that try to get related
objects for more than 1000 objects thus breaking the limit. Django now
splits the related object fetching into batches with at most 1000
parameters.
The tests and patch include some work done by Trac alias NiGhTTraX in
ticket #21205.
