Avoid unnecessary prompting for a default value on ManyToManyField removals.

Author: charettes

CHANGELOG.rst

@@ -1,3 +1,11 @@
+1.2.1
+=====
+
+:release-date: not-released
+
+- Avoid unnecessary prompting for a default value on `ManyToManyField`
+  removals. (#59)
+
 1.2.0
 =====
 

syzygy/autodetector.py

@@ -218,9 +218,14 @@ def _generate_added_field(self, app_label, model_name, field_name):
     def _generate_removed_field(self, app_label, model_name, field_name):
         field = self.from_state.models[app_label, model_name].fields[field_name]
         remove_default = field.default
-        if (remove_default is NOT_PROVIDED and field.null) or getattr(
-            field, "db_default", NOT_PROVIDED
-        ) is not NOT_PROVIDED:
+        if (
+            # Nullable fields will use null if not specified.
+            (remove_default is NOT_PROVIDED and field.null)
+            # Fields with a db_default will use the value if not specified.
+            or getattr(field, "db_default", NOT_PROVIDED) is not NOT_PROVIDED
+            # Many-to-many fields are not backend by concrete columns.
+            or field.many_to_many
+        ):
             return super()._generate_removed_field(app_label, model_name, field_name)
 
         if remove_default is NOT_PROVIDED:

tests/test_autodetector.py

@@ -159,6 +159,19 @@ def test_field_removal(self):
             with self.subTest(field=field):
                 self._test_field_removal(field)
 
+    def test_many_to_many_removal(self):
+        from_model = ModelState(
+            "tests", "Model", [("field", models.ManyToManyField("self"))]
+        )
+        to_model = ModelState("tests", "Model", [])
+        changes = self.get_changes([from_model], [to_model])["tests"]
+        self.assertEqual(len(changes), 1)
+        self.assertEqual(get_migration_stage(changes[0]), Stage.POST_DEPLOY)
+        self.assertEqual(changes[0].dependencies, [])
+        self.assertEqual(len(changes[0].operations), 1)
+        operation = changes[0].operations[0]
+        self.assertIsInstance(operation, migrations.RemoveField)
+
     def test_nullable_field_removal(self):
         """
         No action required if the field is already NULL'able and doesn't have