i have a situation, where using select_related with depth=1 or depth=2 gives wrong results.
increasing depth to 3, or leaving out the depth parameter gives correct results.
the data to reproduce the problem:
models.py: (for this test-case, i assume that it is in the app called 'myapp')
from django.db.models import Model, ForeignKey, CharField
class Newsletter(Model):
name = CharField(maxlength=128)
class Team(Model):
name = CharField(maxlength=128)
class Group(Model):
team = ForeignKey(Team)
class User(Model):
group = ForeignKey(Group)
class Subscription(Model):
user = ForeignKey(User)
newsletter = ForeignKey(Newsletter)
use the following commands to trigger the problem:
from myapp import models
team = models.Team.objects.create(name='team')
group = models.Group.objects.create(team=team)
user = models.User.objects.create(group=group)
newsletter = models.Newsletter.objects.create(name='newsletter')
subscription = models.Subscription.objects.create(user=user, newsletter=newsletter)
q = models.Subscription.objects.filter(id=1)
print q[0].newsletter.name
print q.select_related(depth=0)[0].newsletter.name
print q.select_related(depth=1)[0].newsletter.name
print q.select_related(depth=2)[0].newsletter.name
print q.select_related(depth=3)[0].newsletter.name
it's output is
newsletter
newsletter
1
team
newsletter
the third and fourth line from the output ("1" and "team") are clearly wrong, they should all give the same result.
notes:
1. tested on mac-osx with sqlite3 and postgresql8.2 with both psycopg1 and psycopg2 (from macports) (problem was also reproducible on ubuntu-linux). package versions for the mac-osx:
- django: 5620
- python: 2.4.4
- sqlite3: 3.4.0
- pysqlite: 2.3.3
- psycopg: 1.1.21
- psycopg2: 2.0.5
- postgresql: 8.2.4
2. this is the shortest test-case i could come up with. if i make the "foreignkey-chain" shorter, the problem does not show up.
3. after examining the sql-queries that are generated for the 'wrong' queryset, it seems that the correct sql-query is generated, so probably the sql-query-result is incorrectly mapped to the objects.
4. this problem might be the same as the one discussed in #3623, but i am not sure, and also my test-case is smaller, so maybe easier to use.
