Fixed #19432 -- Provided better error message for get_object_or_404

Thanks Kit Sunde for the report and Brian Holdefehr for the initial
patch.

django/shortcuts/__init__.py

@@ -7,6 +7,7 @@ for convenience's sake.
 from django.template import loader, RequestContext
 from django.http import HttpResponse, Http404
 from django.http import HttpResponseRedirect, HttpResponsePermanentRedirect
+from django.db.models.base import ModelBase
 from django.db.models.manager import Manager
 from django.db.models.query import QuerySet
 from django.core import urlresolvers
@@ -72,13 +73,20 @@ def _get_queryset(klass):
     """
     Returns a QuerySet from a Model, Manager, or QuerySet. Created to make
     get_object_or_404 and get_list_or_404 more DRY.
+
+    Raises a ValueError if klass is not a Model, Manager, or QuerySet.
     """
     if isinstance(klass, QuerySet):
         return klass
     elif isinstance(klass, Manager):
         manager = klass
-    else:
+    elif isinstance(klass, ModelBase):
         manager = klass._default_manager
+    else:
+        klass__name = klass.__name__ if isinstance(klass, type) \
+                      else klass.__class__.__name__
+        raise ValueError("Object is of type '%s', but must be a Django Model, "
+                         "Manager, or QuerySet" % klass__name)
     return manager.all()
 
 def get_object_or_404(klass, *args, **kwargs):

tests/modeltests/get_object_or_404/tests.py

@@ -80,3 +80,28 @@ class GetObjectOr404Tests(TestCase):
             get_list_or_404(Article.objects.all(), title__icontains="Run"),
             [article]
         )
+
+    def test_bad_class(self):
+        # Given an argument klass that is not a Model, Manager, or Queryset
+        # raises a helpful ValueError message
+        self.assertRaisesMessage(ValueError,
+            "Object is of type 'str', but must be a Django Model, Manager, "
+            "or QuerySet",
+            get_object_or_404, "Article", title__icontains="Run"
+        )
+
+        class CustomClass(object):
+            pass
+
+        self.assertRaisesMessage(ValueError,
+            "Object is of type 'CustomClass', but must be a Django Model, "
+            "Manager, or QuerySet",
+            get_object_or_404, CustomClass, title__icontains="Run"
+        )
+
+        # Works for lists too
+        self.assertRaisesMessage(ValueError,
+            "Object is of type 'list', but must be a Django Model, Manager, "
+            "or QuerySet",
+            get_list_or_404, [Article], title__icontains="Run"
+        )