Migration questioner complains about missing defaults for fields in unmanaged models

[Jacob Walls]

Since the improvement to tracking unmanaged model field alterations in #35813, the migration questioner (the interactive prompt) will now complain on missing defaults for altered fields.

In ​a post-merge comment I suggested we could short-circuit in the questioner for unmanaged models, since if the model is unmanaged then it's not strictly true that it's "impossible" to add such fields, especially for unmanaged models that just shadow database views.

Sarah had a ​similar observation before merge.

With this patch, I no longer needed to enter dummy values in the prompt:

django/db/migrations/autodetector.py

@@ -1163 +1163 @@
             or (field.blank and field.empty_strings_allowed)
             or (isinstance(field, time_fields) and field.auto_now)
             or (isinstance(field, auto_fields))
+            or not self.to_state.apps.get_model(app_label, model_name)._meta.managed
         )
         if not preserve_default:
             field = field.clone()
@@ -1331 +1332 @@
                         and not new_field.has_default()
                         and not new_field.has_db_default()
                         and not new_field.many_to_many
+                        and self.to_state.apps.get_model(app_label, model_name)._meta.managed
                     ):
                         field = new_field.clone()
                         new_default = self.questioner.ask_not_null_alteration(

There would be a few other places to check to see where else we can short-circuit. What do folks think?

[Natalia Bidart]

Thank you!

[Jacob Walls <jacobtylerwalls@…>]

In 8f52e919:

Fixed #37224 -- Skipped questioner for field changes on unmanaged models.