Indexes of only the first abstract base class are included in the model

[Dmitry Ulupov]

If model has multiple base abstract models, their Meta.indexes declarations are treated differently.

Only indexes from the first class are taken into account.
Indexes of all other base classes are ignored.

Consider this code:

class ParentA(models.Model):
    field_a = models.CharField(max_length=10)

    class Meta:
        abstract = True


class ParentB(models.Model):
    field_b = models.CharField(max_length=10)

    class Meta:
        abstract = True
        indexes = [
            models.Index(
                fields=["field_b"],
                name="ix_%(app_label)s_%(class)s",
            ),
        ]


class ChildOf_A_B(ParentA, ParentB):
    pass


class ChildOf_B_A(ParentB, ParentA):
    pass

makemigrations in this case produces this:

./manage.py makemigrations app

Migrations for 'app':
  project/app/migrations/0001_initial.py
    - Create model ChildOf_A_B
    - Create model ChildOf_B_A
    - Create index ix_app_childof_b_a on field(s) field_b of model childof_b_a

So index on ChildOf_B_A is created, but on ChildOf_A_B is not.
And only difference is the order of declaration of the base classes.

[Dmitry Ulupov]

Just finished re-reading the "multiple inheritance" section and this is an expected behaviour.
First class indeed clobbers all others and indexes declaration is lost.
Solution is not to have such convoluted structure as I have.