Refactor UpdateModelMixin.update

Reduce nesting, return early in error cases.

rest_framework/mixins.py

@@ -116,30 +116,27 @@ class UpdateModelMixin(object):
         partial = kwargs.pop('partial', False)
         self.object = self.get_object_or_none()
 
-        if self.object is None:
-            created = True
-            save_kwargs = {'force_insert': True}
-            success_status_code = status.HTTP_201_CREATED
-        else:
-            created = False
-            save_kwargs = {'force_update': True}
-            success_status_code = status.HTTP_200_OK
-
         serializer = self.get_serializer(self.object, data=request.DATA,
                                          files=request.FILES, partial=partial)
 
-        if serializer.is_valid():
+        if not serializer.is_valid():
+            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+
         try:
             self.pre_save(serializer.object)
         except ValidationError as err:
             # full_clean on model instance may be called in pre_save, so we
             # have to handle eventual errors.
             return Response(err.message_dict, status=status.HTTP_400_BAD_REQUEST)
-            self.object = serializer.save(**save_kwargs)
-            self.post_save(self.object, created=created)
-            return Response(serializer.data, status=success_status_code)
 
-        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+        if self.object is None:
+            self.object = serializer.save(force_insert=True)
+            self.post_save(self.object, created=True)
+            return Response(serializer.data, status=status.HTTP_201_CREATED)
+        else:
+            self.object = serializer.save(force_update=True)
+            self.post_save(self.object, created=False)
+            return Response(serializer.data, status=status.HTTP_200_OK)
 
     def partial_update(self, request, *args, **kwargs):
         kwargs['partial'] = True