[1.0.X] Added a test from Jamie Gennis to ensure #9848 doesn't reappear.

The bug itself was fixed at some point in the past months (there have
been a few improvements to update() recently). Fixed #9848. 

(Merge of r10528 from trunk.  Per comment in #9848 the fix was in r9967,
which was backported in r9968, thus it seems right to backport the new
test as well.)


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10607 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/queries/models.py

@@ -1096,6 +1096,23 @@ def __unicode__(self):
 >>> list(Note.objects.filter(pk__in=g())) == [n_obj]
 True
 
+Make sure that updates which only filter on sub-tables don't inadvertently
+update the wrong records (bug #9848).
+
+# Make sure that the IDs from different tables don't happen to match.
+>>> Ranking.objects.filter(author__name='a1')
+[<Ranking: 3: a1>]
+>>> Ranking.objects.filter(author__name='a1').update(rank='4')
+1
+>>> r = Ranking.objects.filter(author__name='a1')[0]
+>>> r.id != r.author.id
+True
+>>> r.rank
+4
+>>> r.rank = 3
+>>> r.save()
+>>> Ranking.objects.all()
+[<Ranking: 3: a1>, <Ranking: 2: a2>, <Ranking: 1: a3>]
 """}
 
 # In Python 2.3 and the Python 2.6 beta releases, exceptions raised in __len__