Reverse FK conditions filter queryset when used in case statements in some cases

[Matt d'Entremont]

I'm running into some odd behaviour with the new conditional support added in 1.8.

My use case is the following:

• Annotate a queryset with the count of reverse FKs, matching a condition

This works fine given a many-to-one relationship, however not with many-to-one/none.

With the many-to-one/none, it appears an INNER JOIN is made, which removes objects from my queryset which an empty reverse FK set.

To summarize:

Expected:
Annotate all objects with the a count of reverse FKs matching a condition

Actual:
Annotate only objects objects with 1 or more associated reverse FKs, with a count of the reverse FKs matching a condition

[Matt d'Entremont]

I've added a unit test which demonstrates the issue here: ​https://github.com/django/django/pull/4613

[Anssi Kääriäinen]

I have a guess what could be happening here. The ORM generates joins as INNER JOINs when using build_filter(). We should manually promote those joins to OUTER JOINs afterwards. Can't work on this today, so I'll check this tomorrow.

[Shai Berger]

See also #24766, similar problems with non-aggregating annotations.

[Tim Graham]

The proposed test is similar to the one added with the fix for #24766 and now passes.