Fixed #8036 -- Fixed a case when attempting to traverse non-existent related

instances. We weren't skipping the correct output columns before processing
subsequent existing related instances. Thanks to mrmachine for the test case.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8598 bcc190cf-cafb-0310-a4f2-bffc1f526a37

2 files changed, 45 insertions, 3 deletions

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 2ff1c26344..c5e9cce90a 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -794,8 +794,9 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
     fields = row[index_start:index_end]
     if not [x for x in fields if x is not None]:
         # If we only have a list of Nones, there was not related object.
-        return None, index_end
-    obj = klass(*fields)
+        obj = None
+    else:
+        obj = klass(*fields)
     for f in klass._meta.fields:
         if not select_related_descend(f, restricted, requested):
             continue
@@ -807,7 +808,8 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
                 cur_depth+1, next)
         if cached_row:
             rel_obj, index_end = cached_row
-            setattr(obj, f.get_cache_name(), rel_obj)
+            if obj is not None:
+                setattr(obj, f.get_cache_name(), rel_obj)
     return obj, index_end
 
 
diff --git a/tests/regressiontests/select_related_regress/models.py b/tests/regressiontests/select_related_regress/models.py
index 163dc59164..eca620ccf7 100644
--- a/tests/regressiontests/select_related_regress/models.py
+++ b/tests/regressiontests/select_related_regress/models.py
@@ -49,6 +49,22 @@ class Enrollment(models.Model):
     std = models.ForeignKey(Student)
     cls = models.ForeignKey(Class)
 
+# Models for testing bug #8036.
+class Country(models.Model):
+    name = models.CharField(max_length=50)
+
+class State(models.Model):
+    name = models.CharField(max_length=50)
+    country = models.ForeignKey(Country)
+
+class ClientStatus(models.Model):
+    name = models.CharField(max_length=50)
+
+class Client(models.Model):
+    name = models.CharField(max_length=50)
+    state = models.ForeignKey(State, null=True)
+    status = models.ForeignKey(ClientStatus)
+
 __test__ = {'API_TESTS': """
 Regression test for bug #7110. When using select_related(), we must query the
 Device and Building tables using two different aliases (each) in order to
@@ -100,4 +116,28 @@ separate).
 u"std"
 >>> e_related.cls.org.person.user.name
 u"org"
+
+Regression test for bug #8036: the first related model in the tests below
+("state") is empty and we try to select the more remotely related
+state__country. The regression here was not skipping the empty column results
+for country before getting status.
+
+>>> australia = Country.objects.create(name='Australia')
+>>> active = ClientStatus.objects.create(name='active')
+>>> client = Client.objects.create(name='client', status=active)
+
+>>> client.status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related()[0].status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related('state')[0].status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related('state', 'status')[0].status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related('state__country')[0].status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related('state__country', 'status')[0].status
+<ClientStatus: ClientStatus object>
+>>> Client.objects.select_related('status')[0].status
+<ClientStatus: ClientStatus object>
 """}