django一对一左连接为空？
我有类似 django 中的模型：
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()
并且我正在尝试获取没有响应的用户的所有消息，我会用 SQL 编写如下：
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
我认为执行此操作的自然方法是：
u.messages_recieved.filter(response = None)
或
u.messages_recieved.filter(response__message_id__isnull = True)
但生成的 SQL 最终总是这样：
WHERE ("project_message"."recipient_id" = 1 AND "project_message"."id" IS NULL)
我是在做一些愚蠢的事情，还是这是 Django 中的一个错误？
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?
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尝试：
结果查询是：
我认为这是正确的。 它确实执行左外连接，然后检查响应消息 id 为空的行。
效果也很好。
我正在使用 django 1.1 RC，但这应该可以在 1.0+ 中工作。
Try:
the resulting query is:
which I think is proper. It is indeed doing the left outer join and then checking for rows with null response message id.
works fine too.
I'm using django 1.1 RC but this should work in 1.0+.
当我试图实现类似的结果时，我所做的事情是：
Something that I've done when trying to achieve a similar result is: