Fix compatibility with older Django versions

polymorphic/showfields.py

@@ -1,8 +1,15 @@
 # -*- coding: utf-8 -*-
 import django
+import re
 from django.db import models
 from django.utils import six
-from django.utils.six import python_2_unicode_compatible
+
+try:
+    from django.utils.six import python_2_unicode_compatible
+except ImportError:
+    from django.utils.encoding import python_2_unicode_compatible  # Django 1.5
+
+RE_DEFERRED = re.compile('_Deferred_.*')
 
 
 @python_2_unicode_compatible
@@ -95,7 +102,7 @@ class ShowFieldBase(object):
         # ( bool: new section , item-text , separator to use after item )
 
         # start with model name
-        parts = [(True, self._meta.object_name, ':')]
+        parts = [(True, RE_DEFERRED.sub('', self.__class__.__name__), ':')]
 
         # add all regular fields
         self._showfields_add_regular_fields(parts)
@@ -152,8 +159,8 @@ class ShowFieldBase(object):
 
     if django.VERSION < (1, 8):
         def get_deferred_fields(self):
-            from django.db.models import DeferredAttribute
-            return set(attr for attr, value in self.__class__ if isinstance(value, DeferredAttribute))
+            from django.db.models.query_utils import DeferredAttribute
+            return set(attr for attr, value in self.__class__.__dict__.items() if isinstance(value, DeferredAttribute))
 
 
 class ShowFieldType(ShowFieldBase):

polymorphic/tests.py

@@ -1139,10 +1139,11 @@ class PolymorphicTests(TestCase):
         self.assertEqual(result, {'cnt': 2})
 
         # aggregate using **args
-        with self.assertRaisesMessage(AssertionError, 'PolymorphicModel: annotate()/aggregate(): ___ model lookup supported for keyword arguments only'):
-            Model2A.objects.aggregate(Count('Model2B___field2'))
-
-
+        self.assertRaisesMessage(
+            AssertionError,
+            'PolymorphicModel: annotate()/aggregate(): ___ model lookup supported for keyword arguments only',
+            lambda: Model2A.objects.aggregate(Count('Model2B___field2'))
+        )
 
     @skipIf(django.VERSION < (1,8,), "This test needs Django >=1.8")
     def test_polymorphic__complex_aggregate(self):
@@ -1294,7 +1295,7 @@ def qrepr(data):
     """
     Ensure consistent repr() output for the QuerySet object.
     """
-    if isinstance(data, models.QuerySet):
+    if isinstance(data, QuerySet):
         if django.VERSION >= (1, 10):
             return repr(data)
         else: