Fix migration order for fields moved from parent to child

Ensure RemoveField on parent model runs before child CreateModel
to avoid FieldError when moving a field in model inheritance.

Fixes #21890.

django/db/migrations/autodetector.py

@@ -563,6 +563,24 @@ class MigrationAutodetector:
                 if isinstance(base, str) and "." in base:
                     base_app_label, base_name = base.split(".", 1)
                     dependencies.append((base_app_label, base_name, None, True))
+                    # Check if any fields in this model exist in the parent model
+                    # in the old state and need to be removed first (to avoid
+                    # FieldError when a field is moved from parent to child).
+                    if (base_app_label, base_name.lower()) in self.kept_model_keys:
+                        old_base_model_state = self.from_state.models.get(
+                            (base_app_label, base_name.lower())
+                        )
+                        if old_base_model_state:
+                            for field_name in model_state.fields:
+                                if field_name in old_base_model_state.fields:
+                                    # This field exists in the parent in the old state
+                                    # Depend on its removal from the parent
+                                    dependencies.append((
+                                        base_app_label,
+                                        base_name.lower(),
+                                        field_name,
+                                        False
+                                    ))
             # Depend on the other end of the primary key if it's a relation
             if primary_key_rel:
                 dependencies.append((

tests/migrations/test_autodetector.py

@@ -2454,3 +2454,34 @@ class AutodetectorTests(TestCase):
         self.assertNumberMigrations(changes, 'app', 1)
         self.assertOperationTypes(changes, 'app', 0, ['DeleteModel'])
         self.assertOperationAttributes(changes, 'app', 0, 0, name='Dog')
+
+    def test_create_model_with_field_removed_from_base_model(self):
+        """
+        Tests autodetection of field being moved from parent model to child
+        model. The field removal from the parent should be ordered before the
+        child model creation to avoid FieldError.
+        """
+        # Before: Readable model with title field
+        readable_with_field = ModelState('app', 'Readable', [
+            ("id", models.AutoField(primary_key=True)),
+            ("title", models.CharField(max_length=200)),
+        ])
+        # After: Readable without title, Book subclass with title
+        readable_without_field = ModelState('app', 'Readable', [
+            ("id", models.AutoField(primary_key=True)),
+        ])
+        book = ModelState('app', 'Book', [
+            ("readable_ptr", models.OneToOneField(
+                "app.Readable",
+                models.CASCADE,
+                parent_link=True,
+                primary_key=True,
+                auto_created=True,
+            )),
+            ("title", models.CharField(max_length=200)),
+        ], bases=('app.Readable',))
+        changes = self.get_changes([readable_with_field], [readable_without_field, book])
+        self.assertNumberMigrations(changes, 'app', 1)
+        self.assertOperationTypes(changes, 'app', 0, ['RemoveField', 'CreateModel'])
+        self.assertOperationAttributes(changes, 'app', 0, 0, model_name='readable', name='title')
+        self.assertOperationAttributes(changes, 'app', 0, 1, name='Book')