Fix TypeError in save when model inherits from both TimeStampModel and StatusModel. (Fixes GH-465)

CHANGES.rst

@@ -4,6 +4,8 @@ CHANGES
 Next release (tbc)
 ------------------
 - Applied `isort` to codebase (Refs GH-#402)
+- Fix `TypeError` in save when model inherits from both TimeStampModel
+  and StatusModel. (Fixes GH-465)
 
 4.1.0 (2020-11-29)
 ------------------

model_utils/models.py

@@ -32,10 +32,8 @@ class TimeStampedModel(models.Model):
         a parameter to the update field argument.
         """
         update_fields = kwargs.get('update_fields', None)
-        if update_fields is not None:
-            update_fields = set(update_fields)
-            if update_fields:
-                kwargs['update_fields'] = update_fields.union({'modified'})
+        if update_fields:
+            kwargs['update_fields'] = set(update_fields).union({'modified'})
 
         super().save(*args, **kwargs)
 
@@ -74,12 +72,10 @@ class StatusModel(models.Model):
         status_changed field is updated even if it is not given as
         a parameter to the update field argument.
         """
-        if (
-            'update_fields' in kwargs
-            and 'status' in kwargs['update_fields']
-            and 'status_changed' not in kwargs['update_fields']
-        ):
-            kwargs['update_fields'] += ['status_changed']
+        update_fields = kwargs.get('update_fields', None)
+        if update_fields and 'status' in update_fields:
+            kwargs['update_fields'] = set(update_fields).union({'status_changed'})
+
         super().save(*args, **kwargs)
 
     class Meta:

tests/models.py

@@ -447,3 +447,13 @@ class CustomNotPrimaryUUIDModel(models.Model):
 
 class SaveSignalHandlingTestModel(SaveSignalHandlingModel):
     name = models.CharField(max_length=20)
+
+
+class TimeStampWithStatusModel(TimeStampedModel, StatusModel):
+    STATUS = Choices(
+        ("active", _("active")),
+        ("deleted", _("deleted")),
+        ("on_hold", _("on hold")),
+    )
+
+    test_field = models.PositiveSmallIntegerField(default=0)

tests/test_models/test_timestamped_model.py

@@ -4,7 +4,7 @@ from django.test import TestCase
 from freezegun import freeze_time
 from parameterized import parameterized
 
-from tests.models import TimeStamp
+from tests.models import TimeStamp, TimeStampWithStatusModel
 
 
 class TimeStampedModelTests(TestCase):
@@ -149,3 +149,12 @@ class TimeStampedModelTests(TestCase):
             t1.save(update_fields=None)
 
         self.assertEqual(t1.modified, datetime(2020, 1, 2))
+
+    def test_model_inherit_timestampmodel_and_statusmodel(self):
+        with freeze_time(datetime(2020, 1, 1)):
+            t1 = TimeStampWithStatusModel.objects.create()
+
+        with freeze_time(datetime(2020, 1, 2)):
+            t1.save(update_fields=['test_field', 'status'])
+
+        self.assertEqual(t1.modified, datetime(2020, 1, 2))