Fixed the many to many behavior.

rest_framework/serializers.py

@@ -992,6 +992,7 @@ class ModelSerializer(Serializer):
 
         if getattr(obj, '_m2m_data', None):
             for accessor_name, object_list in obj._m2m_data.items():
+                [self.save_object(o) for o in object_list]
                 setattr(obj, accessor_name, object_list)
             del(obj._m2m_data)
 

rest_framework/tests/test_serializer_nested.py

@@ -345,3 +345,31 @@ class NestedModelSerializerUpdateTests(TestCase):
         result = deserialize.object
         result.save()
         self.assertEqual(result.id, john.id)
+
+    def test_creation_with_nested_many_to_many_relation(self):
+        class ManyToManyTargetSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = models.ManyToManyTarget
+
+        class ManyToManySourceSerializer(serializers.ModelSerializer):
+            targets = ManyToManyTargetSerializer(many=True, allow_add_remove=True)
+            class Meta:
+                model = models.ManyToManySource
+
+        data = {
+            'name': 'source',
+            'targets': [{
+                'name': 'target1'
+            }, {
+                'name': 'another target'
+            }]
+        }
+
+        source_count = models.ManyToManySource.objects.count()
+        target_count = models.ManyToManyTarget.objects.count()
+
+        deserialize = ManyToManySourceSerializer(data=data)
+        self.assertTrue(deserialize.is_valid(), deserialize.errors)
+        deserialize.save()
+        self.assertEqual(models.ManyToManySource.objects.count(), source_count + 1)
+        self.assertEqual(models.ManyToManyTarget.objects.count(), target_count + 2)