Fixed creation of objects with reversed M2M relations

rest_framework/serializers.py

@@ -447,6 +447,13 @@ class ModelSerializer(Serializer):
                 setattr(instance, key, val)
             return instance
 
+        # Reversed relation
+        for (obj, model) in self.opts.model._meta.get_all_related_m2m_objects_with_model():
+            field_name = obj.field.related_query_name()
+            if field_name in attrs:
+                self.m2m_data[field_name] = attrs.pop(field_name)
+
+        # Forward relation
         for field in self.opts.model._meta.many_to_many:
             if field.name in attrs:
                 self.m2m_data[field.name] = attrs.pop(field.name)

rest_framework/tests/pk_relations.py

@@ -117,6 +117,24 @@ class PrimaryKeyManyToManyTests(TestCase):
         ]
         self.assertEquals(serializer.data, expected)
 
+    def test_reverse_many_to_many_create(self):
+        data = {'id': 4, 'name': u'target-4', 'sources': [1, 3]}
+        serializer = ManyToManyTargetSerializer(data=data)
+        self.assertTrue(serializer.is_valid())
+        obj = serializer.save()
+        self.assertEquals(serializer.data, data)
+        self.assertEqual(obj.name, u'target-4')
+
+        # Ensure target 4 is added, and everything else is as expected
+        queryset = ManyToManyTarget.objects.all()
+        serializer = ManyToManyTargetSerializer(queryset)
+        expected = [
+            {'id': 1, 'name': u'target-1', 'sources': [1, 2, 3]},
+            {'id': 2, 'name': u'target-2', 'sources': [2, 3]},
+            {'id': 3, 'name': u'target-3', 'sources': [3]},
+            {'id': 4, 'name': u'target-4', 'sources': [1, 3]}
+        ]
+        self.assertEquals(serializer.data, expected)
 
 class PrimaryKeyForeignKeyTests(TestCase):
     def setUp(self):