Ticket #17851: fix-db-field-compare-with-test-docstring.diff

django/db/models/fields/__init__.py

@@ -123 +123 @@
         messages.update(error_messages or {})
         self.error_messages = messages
 
-    def __cmp__(self, other):
+    def __lt__(self, other):
         # This is needed because bisect does not take a comparison function.
-        return cmp(self.creation_counter, other.creation_counter)
+        if isinstance(other, Field):
+            return self.creation_counter < other.creation_counter
+        return NotImplemented
 
     def __deepcopy__(self, memodict):
         # We don't have to deepcopy very much here, since most things are not

tests/modeltests/basic/tests.py

@@ -3 +3 @@
 from datetime import datetime
 
 from django.core.exceptions import ObjectDoesNotExist
-from django.db.models.fields import FieldDoesNotExist
+from django.db.models.fields import Field, FieldDoesNotExist
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.utils.translation import ugettext_lazy
 
@@ -509 +509 @@
 
         s = set([a10, a11, a12])
         self.assertTrue(Article.objects.get(headline='Article 11') in s)
+        
+    def test_field_ordering(self):
+        """
+        Field instances have a `__lt__` comparison function to define an
+        ordering based on their creation. Prior to #17851 this ordering
+        comparison relied on the now unsupported `__cmp__` and was assuming
+        compared objects were both Field instances raising `AttributeError`
+        when it should have returned `NotImplemented`.
+        """
+        f1 = Field()
+        f2 = Field(auto_created=True)
+        f3 = Field()
+        self.assertTrue(f2 < f1)
+        self.assertTrue(f1 < f3)
+        self.assertFalse(f1 == None)
+        self.assertFalse(f2 in (None, 1, ''))
 
     def test_extra_method_select_argument_with_dashes_and_values(self):
         # The 'select' argument to extra() supports names with dashes in