Ensure DynamicRelationField.to_representation is passed correct instance

Author: fdintino

dynamic_rest/fields/fields.py

@@ -268,20 +268,7 @@ def _is_dynamic(self):
         )
 
     def get_attribute(self, instance):
-        serializer = self.serializer
-        model = serializer.get_model()
-
-        # attempt to optimize by reading the related ID directly
-        # from the current instance rather than from the related object
-        if not self.kwargs['many'] and serializer.id_only():
-            return instance
-        elif model is not None:
-            try:
-                return getattr(instance, self.source)
-            except model.DoesNotExist:
-                return None
-        else:
-            return instance
+        return instance
 
     def to_representation(self, instance):
         """Represent the relationship, either as an ID or object."""
@@ -296,18 +283,18 @@ def to_representation(self, instance):
             # try the faster way first:
             if hasattr(instance, source_id):
                 return getattr(instance, source_id)
-            elif model is not None:
-                # this is probably a one-to-one field, or a reverse related
-                # lookup, so let's look it up the slow way and let the
-                # serializer handle the id dereferencing
-                try:
-                    instance = getattr(instance, source)
-                except model.DoesNotExist:
-                    instance = None
 
         # dereference ephemeral objects
         if model is None:
             instance = getattr(instance, source)
+        else:
+            # this is probably a one-to-one field, or a reverse related
+            # lookup, so let's look it up the slow way and let the
+            # serializer handle the id dereferencing
+            try:
+                instance = getattr(instance, source)
+            except model.DoesNotExist:
+                instance = None
 
         if instance is None:
             return None

tests/test_serializers.py

@@ -1,5 +1,5 @@
 import unittest
-from mock import patch
+from mock import patch, Mock
 from collections import OrderedDict
 
 from django.test import TestCase, override_settings
@@ -523,6 +523,30 @@ def test_post_processor(data):
         data = serializer.data
         self.assertTrue(data.get('post_processed'))
 
+    def test_to_representation_passed_model_instance(self):
+        mock_obj = Mock()
+
+        class GroupRelationField(DynamicRelationField):
+            def to_representation(self, instance):
+                mock_obj(instance)
+                # Dead men have no groups
+                if instance.is_dead:
+                    return []
+                return super(GroupRelationField, self).to_representation(instance)
+
+        class UserCustomGroupFieldSerializer(UserSerializer):
+            groups = GroupRelationField(GroupSerializer, many=True, embed=True)
+
+        user = User.objects.create(name='Dead', last_name='Mort', is_dead=True)
+        user.groups.add(*self.fixture.groups)
+
+        data = UserCustomGroupFieldSerializer(
+            user, request_fields={'groups': {'name': True}}
+        ).data
+
+        assert data['groups'] == []
+        mock_obj.assert_called_once_with(user)
+
 
 class TestListSerializer(TestCase):