serializers.Field respects ordering on dicts if it exists. Closes #832

Author: tomchristie

rest_framework/fields.py

@@ -19,6 +19,7 @@
 from django.forms import widgets
 from django.utils.encoding import is_protected_type
 from django.utils.translation import ugettext_lazy as _
+from django.utils.datastructures import SortedDict
 
 from rest_framework import ISO_8601
 from rest_framework.compat import timezone, parse_date, parse_datetime, parse_time
@@ -170,7 +171,11 @@ def to_native(self, value):
         elif hasattr(value, '__iter__') and not isinstance(value, (dict, six.string_types)):
             return [self.to_native(item) for item in value]
         elif isinstance(value, dict):
-            return dict(map(self.to_native, (k, v)) for k, v in value.items())
+            # Make sure we preserve field ordering, if it exists
+            ret = SortedDict()
+            for key, val in value.items():
+                ret[key] = self.to_native(val)
+            return ret
         return smart_text(value)
 
     def attributes(self):

rest_framework/tests/fields.py

@@ -2,13 +2,12 @@
 General serializer field tests.
 """
 from __future__ import unicode_literals
+from django.utils.datastructures import SortedDict
 import datetime
 from decimal import Decimal
-
 from django.db import models
 from django.test import TestCase
 from django.core import validators
-
 from rest_framework import serializers
 from rest_framework.serializers import Serializer
 
@@ -63,6 +62,20 @@ def test_non_auto_pk_fields_not_read_only(self):
         serializer = CharPrimaryKeyModelSerializer()
         self.assertEqual(serializer.fields['id'].read_only, False)
 
+    def test_dict_field_ordering(self):
+        """
+        Field should preserve dictionary ordering, if it exists.
+        See: https://github.com/tomchristie/django-rest-framework/issues/832
+        """
+        ret = SortedDict()
+        ret['c'] = 1
+        ret['b'] = 1
+        ret['a'] = 1
+        ret['z'] = 1
+        field = serializers.Field()
+        keys = list(field.to_native(ret).keys())
+        self.assertEqual(keys, ['c', 'b', 'a', 'z'])
+
 
 class DateFieldTest(TestCase):
     """
@@ -645,4 +658,4 @@ class DecimalSerializer(Serializer):
         s = DecimalSerializer(data={'decimal_field': '12345.6'})
 
         self.assertFalse(s.is_valid())
-        self.assertEqual(s.errors,  {'decimal_field': ['Ensure that there are no more than 4 digits in total.']})
+        self.assertEqual(s.errors,  {'decimal_field': ['Ensure that there are no more than 4 digits in total.']})