[1.7.x] Renamed variables to avoid name collision with import of django.db.models.

        old_keys = set(self.old_model_keys).union(self.old_unmanaged_keys)

        added_models = set(self.new_model_keys) - old_keys

        added_unmanaged_models = set(self.new_unmanaged_keys) - old_keys

        models = chain(

        all_added_models = chain(

            sorted(added_models, key=self.swappable_first_key, reverse=True),

            sorted(added_unmanaged_models, key=self.swappable_first_key, reverse=True)

        )

        for app_label, model_name in models:

        for app_label, model_name in all_added_models:

            model_state = self.to_state.models[app_label, model_name]

            model_opts = self.new_apps.get_model(app_label, model_name)._meta

            # Gather related fields

        new_keys = set(self.new_model_keys).union(self.new_unmanaged_keys)

        deleted_models = set(self.old_model_keys) - new_keys

        deleted_unmanaged_models = set(self.old_unmanaged_keys) - new_keys

        models = chain(sorted(deleted_models), sorted(deleted_unmanaged_models))

        for app_label, model_name in models:

        all_deleted_models = chain(sorted(deleted_models), sorted(deleted_unmanaged_models))

        for app_label, model_name in all_deleted_models:

            model_state = self.from_state.models[app_label, model_name]

            model = self.old_apps.get_model(app_label, model_name)

            if not model._meta.managed: