Fixed #17582 - Added message to DoesNotExist exceptions.

Thanks simon@ for the suggestion and JordanPowell
for the initial patch.

django/db/models/fields/related.py

@@ -201,7 +201,9 @@ class SingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjectDescri
                     setattr(rel_obj, self.related.field.get_cache_name(), instance)
             setattr(instance, self.cache_name, rel_obj)
         if rel_obj is None:
-            raise self.related.model.DoesNotExist
+            raise self.related.model.DoesNotExist("%s has no %s." % (
+                                                  instance.__class__.__name__,
+                                                  self.related.get_accessor_name()))
         else:
             return rel_obj
 
@@ -304,7 +306,8 @@ class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjec
                     setattr(rel_obj, self.field.related.get_cache_name(), instance)
             setattr(instance, self.cache_name, rel_obj)
         if rel_obj is None and not self.field.null:
-            raise self.field.rel.to.DoesNotExist
+            raise self.field.rel.to.DoesNotExist(
+                "%s has no %s." % (self.field.model.__name__, self.field.name))
         else:
             return rel_obj
 

docs/releases/1.6.txt

@@ -277,6 +277,9 @@ Minor features
   a ``SuspiciousOperation`` reaches the WSGI handler to return an
   ``HttpResponseBadRequest``.
 
+* The :exc:`~django.core.exceptions.DoesNotExist` exception now includes a
+  message indicating the name of the attribute used for the lookup.
+
 Backwards incompatible changes in 1.6
 =====================================
 

tests/foreign_object/tests.py

@@ -316,6 +316,11 @@ class MultiColumnFKTests(TestCase):
             list(Article.objects.filter(active_translation__abstract=None)),
             [a1, a2])
 
+    def test_foreign_key_raises_informative_does_not_exist(self):
+        referrer = ArticleTranslation()
+        with self.assertRaisesMessage(Article.DoesNotExist, 'ArticleTranslation has no article'):
+            referrer.article
+
 class FormsTests(TestCase):
     # ForeignObjects should not have any form fields, currently the user needs
     # to manually deal with the foreignobject relation.

tests/one_to_one/tests.py

@@ -22,7 +22,8 @@ class OneToOneTests(TestCase):
         # A Place can access its restaurant, if available.
         self.assertEqual(repr(self.p1.restaurant), '<Restaurant: Demon Dogs the restaurant>')
         # p2 doesn't have an associated restaurant.
-        self.assertRaises(Restaurant.DoesNotExist, getattr, self.p2, 'restaurant')
+        with self.assertRaisesMessage(Restaurant.DoesNotExist, 'Place has no restaurant'):
+            self.p2.restaurant
 
     def test_setter(self):
         # Set the place using assignment notation. Because place is the primary