Fixed #17838 - prefetch_related fails for GenericForeignKeys when related object id is not a CharField/TextField

Thanks to mkai for the report and debugging, and tmitchell and Przemek
Lewandowski for their work on the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17744 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/contenttypes/generic.py

@@ -85,16 +85,16 @@ class GenericForeignKey(object):
             ret_val.extend(ct.get_all_objects_for_this_type(pk__in=fkeys))
 
         # For doing the join in Python, we have to match both the FK val and the
-        # content type, so the 'attr' vals we return need to be callables that
+        # content type, so we use a callable that returns a (fk, class) pair.
-        # will return a (fk, class) pair.
         def gfk_key(obj):
             ct_id = getattr(obj, ct_attname)
             if ct_id is None:
                 return None
             else:
-                return (getattr(obj, self.fk_field),
+                model = self.get_content_type(id=ct_id,
-                        self.get_content_type(id=ct_id,
+                                              using=obj._state.db).model_class()
-                                              using=obj._state.db).model_class())
+                return (model._meta.pk.get_prep_value(getattr(obj, self.fk_field)),
+                        model)
 
         return (ret_val,
                 lambda obj: (obj._get_pk_val(), obj.__class__),

tests/modeltests/prefetch_related/models.py

@@ -125,6 +125,15 @@ class Bookmark(models.Model):
     tags = generic.GenericRelation(TaggedItem)
 
 
+class Comment(models.Model):
+    comment = models.TextField()
+
+    # Content-object field
+    content_type   = models.ForeignKey(ContentType)
+    object_pk      = models.TextField()
+    content_object = generic.GenericForeignKey(ct_field="content_type", fk_field="object_pk")
+
+
 ## Models for lookup ordering tests
 
 

tests/modeltests/prefetch_related/tests.py

@@ -5,7 +5,7 @@ from django.test import TestCase
 
 from .models import (Author, Book, Reader, Qualification, Teacher, Department,
     TaggedItem, Bookmark, AuthorAddress, FavoriteAuthors, AuthorWithAge,
-    BookWithYear, Person, House, Room, Employee)
+    BookWithYear, Person, House, Room, Employee, Comment)
 
 
 class PrefetchRelatedTests(TestCase):
@@ -254,6 +254,14 @@ class GenericRelationTests(TestCase):
             qs = TaggedItem.objects.prefetch_related('content_object')
             list(qs)
 
+    def test_prefetch_GFK_nonint_pk(self):
+        Comment.objects.create(comment="awesome", content_object=self.book1)
+
+        # 1 for Comment table, 1 for Book table
+        with self.assertNumQueries(2):
+            qs = Comment.objects.prefetch_related('content_object')
+            [c.content_object for c in qs]
+
     def test_traverse_GFK(self):
         """
         Test that we can traverse a 'content_object' with prefetch_related() and

tests/regressiontests/comment_tests/tests/model_tests.py

@@ -49,3 +49,10 @@ class CommentManagerTests(CommentTestCase):
         author_comments = list(Comment.objects.for_model(Author.objects.get(pk=1)))
         self.assertEqual(article_comments, [c1, c3])
         self.assertEqual(author_comments, [c2])
+
+    def testPrefetchRelated(self):
+        c1, c2, c3, c4 = self.createSomeComments()
+        # one for comments, one for Articles, one for Author
+        with self.assertNumQueries(3):
+            qs = Comment.objects.prefetch_related('content_object')
+            [c.content_object for c in qs]