Initial work at implementing ReturnDict and ReturnList for nested serializers.

rest_framework/serializers.py

@@ -363,6 +363,8 @@ class Serializer(BaseSerializer):
             attribute = field.get_attribute(instance)
             if attribute is None:
                 value = None
+            elif isinstance(field, Serializer):
+                value = field.__class__(attribute).data
             else:
                 value = field.to_representation(attribute)
             transform_method = getattr(self, 'transform_' + field.field_name, None)
@@ -479,9 +481,11 @@ class ListSerializer(BaseSerializer):
         List of object instances -> List of dicts of primitive datatypes.
         """
         iterable = data.all() if (hasattr(data, 'all')) else data
-        return [
-            self.child.to_representation(item) for item in iterable
-        ]
+        if isinstance(self.child, Serializer):
+            serializer = self.child.__class__
+            return [serializer(item).data for item in iterable]
+        else:
+            return [self.child.to_representation(item) for item in iterable]
 
     def update(self, instance, validated_data):
         raise NotImplementedError(

tests/test_serializer_nested.py

@@ -1,4 +1,5 @@
 from rest_framework import serializers
+from rest_framework.utils.serializer_helpers import ReturnDict
 
 
 class TestNestedSerializer:
@@ -39,6 +40,20 @@ class TestNestedSerializer:
         serializer = self.Serializer()
         assert serializer.data == expected_data
 
+    def test_nested_field_uses_return_dict(self):
+        input_data = {
+            'nested': {
+                'one': '1',
+                'two': '2',
+            }
+        }
+        serializer = self.Serializer(input_data)
+        assert isinstance(serializer.data['nested'], ReturnDict)
+
+    def test_empty_nested_field_uses_return_dict(self):
+        serializer = self.Serializer()
+        assert isinstance(serializer.data['nested'], ReturnDict)
+
 # """
 # Tests to cover nested serializers.