pre_save field in parent models are not called during update in update_or_create

[Gagaro]

With the following models:

class Parent(models.Model):
    modified_at = models.DateTimeField(auto_now=True)


class Child(Parent):
    modified_at_child = models.DateTimeField(auto_now=True)

When calling update_or_create, the pre_save of the modified_at field is not called, and the field is not updated:

# Create

>>> instance, _ = Child.objects.update_or_create(pk=1)
>>> instance.modified_at
datetime.datetime(2024, 11, 6, 14, 1, 11, 52881, tzinfo=datetime.timezone.utc)
>>> instance.modified_at_child
datetime.datetime(2024, 11, 6, 14, 1, 11, 54363, tzinfo=datetime.timezone.utc)


# Update

>>> instance, _ = Child.objects.update_or_create(pk=1)
>>> instance.modified_at
datetime.datetime(2024, 11, 6, 14, 1, 11, 52881, tzinfo=datetime.timezone.utc)
>>> instance.modified_at_child
datetime.datetime(2024, 11, 6, 14, 1, 21, 517245, tzinfo=datetime.timezone.utc)

The regression seems to have happened in ​https://github.com/django/django/commit/6cc0f22a73970dd7c0d29d4d8d2ff9e1cc862b30

Using self.model._meta.concrete_fields instead of self.model._meta.local_concrete_fields seems to solve the issue, but I don't know the internal API well enough to understand all of the implications.

PR : ​https://github.com/django/django/pull/18777