The GenericRelation refactoring removed GenericRelations from
model._meta.many_to_many. This had the side effect of disallowing
editable GenericRelations in ModelForms. Editable GenericRelations
aren't officially supported, but if we don't fix this we don't offer any
upgrade path for those who used the ability to set editable=True
in GenericRelation subclass.
Thanks to Trac alias joshcartme for the report and stephencmd and Loic
for working on this issue.
Backpatch of 0e079e4331a8be4dbd18d5e5776116330b0a5e61 from master.
The patch for #19385 caused a regression in certain generic relations
.exclude() filters if a subquery was needed. The fix contains a
refactoring to how Query.split_exclude() and Query.trim_start()
interact.
Thanks to Trac alias nferrari for the report.
When a GenericRelation was defined on abstract model, queries on childs
of the abstract model didn't work. The problem was in the way fields and
in particular field.rel was copied from models to their children.
The regression was likely caused by #19385. Thanks to Gavin Wahl for
spotting the regression.
