如何将 order_by 与 last_added manytomanyfield 一起使用？

Question

模型.py

class ChatRoomId(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    created_date = models.DateTimeField(auto_now_add=True)
    

class MessageContent(models.Model):
    content = models.TextField(blank=True)
    created_date = models.DateTimeField(auto_now_add=True)
    modified_date = models.DateTimeField(auto_now=True)
    

class PersonalMessage(models.Model):
    message = models.ForeignKey(MessageContent, on_delete=models.CASCADE)
    sender = models.ForeignKey(CustomUser, on_delete=models.DO_NOTHING)


class PersonalRoom(models.Model):
    room_id = models.ForeignKey(ChatRoomId, on_delete=models.CASCADE)
    user = models.ManyToManyField(CustomUser)
    message_list = models.ManyToManyField(PersonalMessage)
    modified_date = models.DateTimeField(auto_now=True)

如何通过值"message__created_date" ManyToManyField last added message_list object 对这个查询集PersonalRoom.objects.all()进行排序，即last_item = message_list.all().order_by('-message__created_date')[0] 。

我的想法是

PersonalRoom.objects.all().order_by(
    Subquery(
        PersonalRoom.objects.get(pk=OuterRef('pk')).message_list.all().order_by('-message__created_date')[0]
    )
)

但这会导致错误。

Answer 1

尝试反向关系，如：

PersonalRoom.objects.all().order_by('-message_list__message__created_date')

Answer 2

模型.py

class PersonalRoom(models.Model):
    room_id = models.ForeignKey(ChatRoomId, on_delete=models.CASCADE)
    user = models.ManyToManyField(CustomUser)
    message_list = models.ManyToManyField(PersonalMessage)
    modified_date = models.DateTimeField(auto_now=True)

    @property
    def last_message_date(self):
        _message = self.message_list.all().order_by('-message__created_date')[0]
        _date = _message.message.created_date
        return _date

视图.py

_rooms = PersonalRoom.objects.filter(user__in=[request.user], message_list__isnull=False).distinct()
sorted_rooms = sorted(_rooms, key=lambda item: item.last_message_date, reverse=True)

sorted_rooms是反向排序的 PersonalRoom，其中所有与用户相关的房间模型都按最后添加的带有创建日期的消息进行排序。