django one-to-one left join is null?

Question

I've got models like those in django:

class User(models.Model):
  name = models.CharField(max_length = 128)

class Message(models.Model):
  sender = models.ForeignKey(User, related_name = 'messages_sent')
  recipient = models.ForeignKey(User, related_name = 'messages_recieved')
  subject = models.CharField(max_length = 128)
  body = models.CharField(max_length = 3500)

class Response(models.Model):
  message = models.OneToOneField(Message, primary_key = True)
  reply = models.TextField()

and I'm trying to get all the messages for the user that have no response, something I would write in SQL as:

select * from user u
         join message m on (u.id = m.recipient_id)
         left join response r on (m.id = r.message_id)
where r.message_id = null

I'd think the natural way to do this would be:

u.messages_recieved.filter(response = None)

or

u.messages_recieved.filter(response__message_id__isnull = True)

but the SQL generated always ends up being:

WHERE ("project_message"."recipient_id" = 1  AND "project_message"."id" IS NULL)

Am I doing something stupid, or is this a bug in Django?

Answer 1

Something that I've done when trying to achieve a similar result is:

u.messages_received.filter(~Q(response__id__gt=0))

Answer 2

Try:

user.messages_recieved.filter(response__isnull=True)

the resulting query is:

SELECT "messaging_message"."id", "messaging_message"."sender_id", "messaging_message"."recipient_id", "messaging_message"."subject", "messaging_message"."body" FROM "messaging_message" LEFT OUTER JOIN "messaging_response" ON ("messaging_message"."id" = "messaging_response"."message_id") WHERE ("messaging_message"."recipient_id" = 1  AND "messaging_response"."message_id" IS NULL)

which I think is proper. It is indeed doing the left outer join and then checking for rows with null response message id.

u.messages_recieved.filter(response=None)

works fine too.

I'm using django 1.1 RC but this should work in 1.0+.