UpdateQuery.add_update_values always computes "direct" variable as True

[Ryan P Kilby]

For context, I've been messing around with ForeignObject in an attempt to use correlated subqueries as a join condition. e.g., defining a latest_post relation field that enables queries like Author.objects.select_related("latest_post"). Given that the relation is based on a subquery, the field is not concrete, and in testing how the queryset API works with this field, I ran into a confusing condition in QuerySet.update via the UpdateQuery.add_update_values method. In short, ​line 90 computes a direct variable that always resolves to true. You can verify how the boolean logic resolves with:

class UpdateTests(unittest.TestCase):

    def test_direct(self):
        testcases = [
            (True, True),
            (True, False),
            (False, True),
            (False, False),
        ]
        for auto_created, concrete in testcases:
            with self.subTest(auto_created=auto_created, concrete=concrete):
                self.assertTrue(not (auto_created and not concrete) or not concrete)

This condition should simplify to not auto_created or concrete or not concrete to concrete or not concrete to True. Digging through the blame, direct was previously provided by the model meta's .get_field_by_name(), which ​states "direct is True if the field exists on this model". Without fully understanding the field internals, I assume direct should have been replaced with just field.concrete. I'm not sure what the intent was for auto-created fields, but whether it's concrete seems to be the actual relevant bit, not whether it's auto-created.

[Jacob Walls <jacobtylerwalls@…>]

In 11c2c9a:

Refs #36481 -- Improved test coverage for invalid updates on reverse relations.

[Jacob Walls <jacobtylerwalls@…>]

In bad03eb:

Fixed #36481 -- Fixed QuerySet.update concrete fields check.

FieldError is now emitted for invalid update calls involving reverse
relations, where previously they failed with AttributeError.