Question

I am having trouble getting a Django ORM query to work correctly. I have this Friendship model:

class Friendship(models.Model):
    user1 = models.ForeignKey(User, related_name='friendships1')
    user2 = models.ForeignKey(User, related_name='friendships2')
    class Meta:
        unique_together = ('user1', 'user2',)

To find the friends for a given user, we have to check user1 and user2 because we can never be sure what side of the relationship they will be on. So, to get all friends for a given user, I use the following query:

user = request.user
User.objects.filter(
    Q(friendships1__user2=user, friendships1__status__in=statuses) |
    Q(friendships2__user1=user, friendships2__status__in=statuses)
)

This seems to me like it should work, but it does not. It gives me duplicates. Here is the SQL that it generates:

SELECT auth_user.*
FROM auth_user
LEFT OUTER JOIN profile_friendship ON (auth_user.id = profile_friendship.user1_id)
LEFT OUTER JOIN profile_friendship T4 ON (auth_user.id = T4.user2_id)
WHERE (
    (profile_friendship.status IN ('Accepted') AND profile_friendship.user2_id = 1 )
    OR (T4.user1_id = 1 AND T4.status IN ('Accepted'))
);

Here is the SQL that I want, which produces correct results:

SELECT f1.id as f1id, f2.id AS f2id, u.*
FROM auth_user u
LEFT OUTER JOIN profile_friendship f1 ON (u.id = f1.user1_id AND f1.user2_id = 1 AND f1.status IN ('Accepted'))
LEFT OUTER JOIN profile_friendship f2 ON (u.id = f2.user2_id AND f2.user1_id = 1 AND f2.status IN ('Accepted'))
WHERE f1.id IS NOT NULL OR f2.id IS NOT NULL

I know I can do this in a raw query, but then I don’t think I’ll be able to chain. Is there a nice clean way to do this without going raw?

Answer 1

Simple solution:

user = request.user
User.objects.filter(
    Q(friendships1__user2=user, friendships1__status__in=statuses) |
    Q(friendships2__user1=user, friendships2__status__in=statuses)
).distinct()

Anyone know any drawback?