Optimizations play nicely with select_related, prefetch_related

rest_framework/relations.py

@@ -101,17 +101,7 @@ class RelatedField(Field):
 
     def get_iterable(self, instance, source_attrs):
         relationship = get_attribute(instance, source_attrs)
-        relationship = relationship.all() if (hasattr(relationship, 'all')) else relationship
-
-        if self.use_pk_only_optimization():
-            # Optimized case, return mock objects only containing the pk attribute.
-            return [
-                PKOnlyObject(pk=pk)
-                for pk in relationship.values_list('pk', flat=True)
-            ]
-
-        # Standard case, return the object instances.
-        return relationship
+        return relationship.all() if (hasattr(relationship, 'all')) else relationship
 
     @property
     def choices(self):

tests/test_relations_hyperlink.py

@@ -92,6 +92,12 @@ class HyperlinkedManyToManyTests(TestCase):
         with self.assertNumQueries(4):
             self.assertEqual(serializer.data, expected)
 
+    def test_many_to_many_retrieve_prefetch_related(self):
+        queryset = ManyToManySource.objects.all().prefetch_related('targets')
+        serializer = ManyToManySourceSerializer(queryset, many=True, context={'request': request})
+        with self.assertNumQueries(2):
+            serializer.data
+
     def test_reverse_many_to_many_retrieve(self):
         queryset = ManyToManyTarget.objects.all()
         serializer = ManyToManyTargetSerializer(queryset, many=True, context={'request': request})

tests/test_relations_pk.py

@@ -71,6 +71,12 @@ class PKManyToManyTests(TestCase):
         with self.assertNumQueries(4):
             self.assertEqual(serializer.data, expected)
 
+    def test_many_to_many_retrieve_prefetch_related(self):
+        queryset = ManyToManySource.objects.all().prefetch_related('targets')
+        serializer = ManyToManySourceSerializer(queryset, many=True)
+        with self.assertNumQueries(2):
+            serializer.data
+
     def test_reverse_many_to_many_retrieve(self):
         queryset = ManyToManyTarget.objects.all()
         serializer = ManyToManyTargetSerializer(queryset, many=True)
@@ -188,6 +194,12 @@ class PKForeignKeyTests(TestCase):
         with self.assertNumQueries(3):
             self.assertEqual(serializer.data, expected)
 
+    def test_reverse_foreign_key_retrieve_prefetch_related(self):
+        queryset = ForeignKeyTarget.objects.all().prefetch_related('sources')
+        serializer = ForeignKeyTargetSerializer(queryset, many=True)
+        with self.assertNumQueries(2):
+            serializer.data
+
     def test_foreign_key_update(self):
         data = {'id': 1, 'name': 'source-1', 'target': 2}
         instance = ForeignKeySource.objects.get(pk=1)

tests/test_relations_slug.py

@@ -54,7 +54,14 @@ class SlugForeignKeyTests(TestCase):
             {'id': 2, 'name': 'source-2', 'target': 'target-1'},
             {'id': 3, 'name': 'source-3', 'target': 'target-1'}
         ]
-        self.assertEqual(serializer.data, expected)
+        with self.assertNumQueries(4):
+            self.assertEqual(serializer.data, expected)
+
+    def test_foreign_key_retrieve_select_related(self):
+        queryset = ForeignKeySource.objects.all().select_related('target')
+        serializer = ForeignKeySourceSerializer(queryset, many=True)
+        with self.assertNumQueries(1):
+            serializer.data
 
     def test_reverse_foreign_key_retrieve(self):
         queryset = ForeignKeyTarget.objects.all()
@@ -65,6 +72,12 @@ class SlugForeignKeyTests(TestCase):
         ]
         self.assertEqual(serializer.data, expected)
 
+    def test_reverse_foreign_key_retrieve_prefetch_related(self):
+        queryset = ForeignKeyTarget.objects.all().prefetch_related('sources')
+        serializer = ForeignKeyTargetSerializer(queryset, many=True)
+        with self.assertNumQueries(2):
+            serializer.data
+
     def test_foreign_key_update(self):
         data = {'id': 1, 'name': 'source-1', 'target': 'target-2'}
         instance = ForeignKeySource.objects.get(pk=1)