queryset-refactor: Fixed a possibility of shooting oneself in the foot and

creating infinite recursion with select_related(). Refs #3045, #3288.


git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@6521 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/query.py

@@ -294,7 +294,8 @@ class _QuerySet(object):
         """Returns a new QuerySet instance that will select related objects."""
         obj = self._clone()
         obj.query.select_related = true_or_false
-        obj.query.max_depth = depth
+        if depth:
+            obj.query.max_depth = depth
         return obj
 
     def order_by(self, *field_names):

django/db/models/sql/query.py

@@ -87,7 +87,10 @@ class Query(object):
         self.low_mark, self.high_mark = 0, None  # Used for offset/limit
         self.distinct = False
         self.select_related = False
-        self.max_depth = 0
+
+        # Arbitrary maximum limit for select_related to prevent infinite
+        # recursion. Can be changed by the depth parameter to select_related().
+        self.max_depth = 5
 
         # These are for extensions. The contents are more or less appended
         # verbatim to the appropriate clause.

tests/regressiontests/queries/models.py

@@ -80,6 +80,14 @@ class Cover(models.Model):
     def __unicode__(self):
         return self.title
 
+# Some funky cross-linked models for testing a couple of infinite recursion
+# cases.
+class X(models.Model):
+    y = models.ForeignKey('Y')
+
+class Y(models.Model):
+    x1 = models.ForeignKey(X, related_name='y1')
+
 __test__ = {'API_TESTS':"""
 >>> t1 = Tag(name='t1')
 >>> t1.save()
@@ -353,9 +361,18 @@ True
 >>> ExtraInfo.objects.values('note')
 [{'note': 1}, {'note': 2}]
 
-# Bug 5261
+Bug #5261
 >>> Note.objects.exclude(Q())
 [<Note: n1>, <Note: n2>, <Note: n3>]
 
+Bug #3045, #3288
+Once upon a time, select_related() with circular relations would loop
+infinitely if you forgot to specify "depth". Now we set an arbitrary default
+upper bound.
+>>> X.objects.all()
+[]
+>>> X.objects.select_related()
+[]
+
 """}