Warn about ordering field use

Author: Ryan P Kilby

README.rst

@@ -280,6 +280,13 @@ Yes you can.  `django-rest-framework-filters` extends `django-filter`, and you c
 ``django-rest-framework-filters``, but you can use ``RelatedFilter`` to
 link to a filter relation defined elsewhere that uses vanilla ``django-filter``.
 
+Caveats
+~~~~~~~
+
+djangorestframework-filters is not compatible with the filterset's `order_by`
+meta option. Use `rest_framework.filters.OrderingFilter` instead if you need
+to support ordering.
+
 
 License
 -------

rest_framework_filters/filterset.py

@@ -39,6 +39,16 @@ def __new__(cls, name, bases, attrs):
         new_class = super(FilterSetMetaclass, cls).__new__(cls, name, bases, attrs)
         fix_filter_field = _get_fix_filter_field(new_class)
 
+        # order_by is not compatible.
+        if new_class._meta.order_by:
+            new_class._meta.order_by = False
+            warnings.warn(
+                'order_by is no longer supported. Use '
+                'rest_framework.filters.OrderingFilter instead. See: '
+                'https://github.com/philipn/django-rest-framework-filters/issues/62',
+                DeprecationWarning, stacklevel=2
+            )
+
         # Populate our FilterSet fields with all the possible
         # filters for the AllLookupsFilter field.
         for name, filter_ in six.iteritems(new_class.base_filters.copy()):

tests/test_deprecations.py

@@ -61,6 +61,22 @@ class F(FilterSet):
             self.assertEqual(len(w), 0)
 
 
+class OrderByDeprecationTests(TestCase):
+
+    def test_override_notifcation(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+
+            class F(FilterSet):
+                class Meta:
+                    model = User
+                    order_by = 'username'
+
+            F().qs
+            self.assertEqual(len(w), 1)
+            self.assertTrue(issubclass(w[-1].category, DeprecationWarning))
+
+
 class AllLookupsDeprecationTests(TestCase):
 
     def test_ALL_LOOKUPS_notification(self):