RelatedManager.all().get_or_create() does not work

[Nick Pope]

When accessing the queryset for a related manager, .get_or_create() and .update_or_create() lose context of the related instance.

Calling on the related manager works as expected:

publisher.books.get_or_create(name="The Very Hungry Caterpillar")

This is the case that was fixed by #3121 and #23611.

But calling on the queryset causes an IntegrityError to be raised:

publisher.books.all().get_or_create(name="The Very Hungry Caterpillar")

This can be a subtle failure that is hard to understand, especially if publisher.books.all() is assigned to a variable earlier.

The challenge here is that the overridden methods on the manager set kwargs[self.field.name] = self.instance.

We'd need to be able to pass this information down to the queryset. It looks like this might already be available in _known_related_objects which is set by RelatedManager._apply_rel_filters(), so that would be a good starting point for investigation.

If this is something we can't fix reliably, then we should update the admonition under ​.get_or_create() in the docs and probably update ​.update_or_create() to make this and other issues related to use through RelatedManager more clear.