Allow provision for ordering fields when setting them.

When deserializing Django objects, reverse relations need to be deserialized after primary key field

Fixes clarkduvall#3

serpy/serializer.py

@@ -56,21 +56,32 @@ def _compile_meta(direct_fields, serializer_meta, serializer_cls):
         # get the right order of meta bases
         meta_bases = meta_bases[::-1]
 
+        # automatically create an inner-class Meta that inherits from
+        # parent class's inner-class Meta
+        Meta = type('Meta', meta_bases, {})
+        meta = Meta()
+
         compiled_read_fields = [
             _compile_read_field_to_tuple(field, name, serializer_cls)
             for name, field in field_map.items()
             ]
 
+        field_map_items = []
+        if not meta.override_deser_field_order:
+            field_map_items = field_map.items()
+        else:
+            for field in meta.override_deser_field_order:
+                field_map_items.append((field, field_map[field]))
+            for name, field in field_map.items():
+                if name not in meta.override_deser_field_order:
+                    field_map_items.append((name, field))
+
         compiled_write_fields = [
             _compile_write_field_to_tuple(field, name, serializer_cls)
-            for name, field in field_map.items()
+            for name, field in field_map_items
             if not field.read_only
             ]
 
-        # automatically create an inner-class Meta that inherits from
-        # parent class's inner-class Meta
-        Meta = type('Meta', meta_bases, {})
-        meta = Meta()
         meta._field_map = field_map
         meta._compiled_read_fields = compiled_read_fields
         meta._compiled_write_fields = compiled_write_fields
@@ -142,10 +153,19 @@ class FooSerializer(Serializer):
     """
     # Inner-class
     class Meta(object):
+        # class of the deserialized object
         cls = None
+
+        # default getter to use for getting field values
         default_getter = operator.attrgetter
+
+        # default setter to use for setting field values
         default_setter = attrsetter
 
+        # override some fields to be ordered before others
+        # can also be used to order all fields
+        override_deser_field_order = []
+
     def __init__(self, instance=None, data=None, many=False, **kwargs):
         super(Serializer, self).__init__(**kwargs)
         self._can_serialize = instance is not None

tests/test_serializer.py

@@ -1,3 +1,4 @@
+import collections
 import unittest
 
 from serpy.fields import Field, MethodField, IntField, FloatField, StrField
@@ -367,6 +368,36 @@ class Meta:
         self.assertRaises(AttributeError,
                           lambda: serializer.deserialized_value)
 
+    def test_serializer_field_ordering(self):
+        class OrderedDictObj(collections.OrderedDict):
+            def __setattr__(self, name, value):
+                if not name.startswith('_'):
+                    self[name] = value
+                else:
+                    super(OrderedDictObj, self).__setattr__(name, value)
+
+        class ASerializer(Serializer):
+            class Meta:
+                cls = OrderedDictObj
+                override_deser_field_order = ['a']
+
+            a = IntField()
+            b = IntField()
+
+        class BSerializer(Serializer):
+            class Meta:
+                cls = OrderedDictObj
+                override_deser_field_order = ['b']
+
+            a = IntField()
+            b = IntField()
+
+        data = {'a': 1, 'b': 2}
+        a_obj = ASerializer(data=data).deserialized_value
+        b_obj = BSerializer(data=data).deserialized_value
+
+        self.assertEqual(a_obj.keys(), ['a', 'b'])
+        self.assertEqual(b_obj.keys(), ['b', 'a'])
 
 if __name__ == '__main__':
     unittest.main()