Django 聊天室模型：从用户所属的所有房间检索最新消息

Question

我很难构建一个查询（sqlite）来获取用户所属的每个聊天室的最新消息。这是我在 Django 中的模型：

class Membership(models.Model):
    room_name = models.TextField()
    members = models.ManyToManyField(CustomUser, through="Message")

class Message(models.Model):
    user = models.ForeignKey(CustomUser, on_delete=models.CASCADE)
    room = models.ForeignKey(Membership, on_delete=models.CASCADE)
    advertisement = models.ForeignKey(Advertisement, on_delete=models.CASCADE, default=None)
    message = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)

class CustomUser(AbstractUser):
    username = models.CharField(max_length=200, unique=False)

现在考虑到这一点，我想显示用户所属的所有房间以及房间中的最新消息。我感觉我已经很接近了:

select *
from chat_message as cm
inner join (select max(id) as lm from chat_message group by room_id) as last_messages on last_messages.lm = cm.id
inner join main_advertisement ma on cm.advertisement_id = ma.id
inner join chat_membership as cmb ON cm.room_id = cmb.id
order by id;

这看起来为我提供了每个房间的最新消息（和其他数据），但现在我很难过滤 1 个用户（例如 user_id = 3）。

任何想法，以及如何在 django ORM 中开始构建它的可能提示，我们将不胜感激。

Answer 1

您可以向内部查询添加一个过滤器，您可以在其中获得最大

chat_message

ids：

select *
from chat_message as cm
inner join (select max(id) as lm from chat_message where user_id = 3 group by room_id) as last_messages on last_messages.lm = cm.id
inner join main_advertisement ma on cm.advertisement_id = ma.id
inner join chat_membership as cmb ON cm.room_id = cmb.id
order by id;