Fixed #21169 -- Reworked RelatedManager methods use default filtering

The `remove()` and `clear()` methods of the related managers created by
`ForeignKey`, `GenericForeignKey`, and `ManyToManyField` suffered from a
number of issues. Some operations ran multiple data modifying queries without
wrapping them in a transaction, and some operations didn't respect default
filtering when it was present (i.e. when the default manager on the related
model implemented a custom `get_queryset()`).

Fixing the issues introduced some backward incompatible changes:

- The implementation of `remove()` for `ForeignKey` related managers changed
  from a series of `Model.save()` calls to a single `QuerySet.update()` call.
  The change means that `pre_save` and `post_save` signals aren't called anymore.

- The `remove()` and `clear()` methods for `GenericForeignKey` related
  managers now perform bulk delete so `Model.delete()` isn't called anymore.

- The `remove()` and `clear()` methods for `ManyToManyField` related
  managers perform nested queries when filtering is involved, which may
  or may not be an issue depending on the database and the data itself.

Refs. #3871, #21174.

Thanks Anssi Kääriäinen and Tim Graham for the reviews.

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 834b849c8f..fa4a09756f 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -2132,6 +2132,8 @@ extract two field values, where only one is expected::
     inner_qs = Blog.objects.filter(name__contains='Ch').values('name', 'id')
     entries = Entry.objects.filter(blog__name__in=inner_qs)
 
+.. _nested-queries-performance:
+
 .. admonition:: Performance considerations
 
     Be cautious about using nested queries and understand your database