我试图制作一个非常简单的Subquery，使用OuterRef(不是为了实际目的，只是为了让它工作)，但我一直遇到同样的错误.
posts/models.py码
from django.db import models
class Tag(models.Model):
name = models.CharField(max_length=120)
def __str__(self):
return self.name
class Post(models.Model):
title = models.CharField(max_length=120)
tags = models.ManyToManyField(Tag)
def __str__(self):
return self.title
manage.py shell码
>>> from django.db.models import OuterRef, Subquery
>>> from posts.models import Tag, Post
>>> tag1 = Tag.objects.create(name='tag1')
>>> post1 = Post.objects.create(title='post1')
>>> post1.tags.add(tag1)
>>> Tag.objects.filter(post=post1.pk)
<QuerySet [<Tag: tag1>]>
>>> tags_list = Tag.objects.filter(post=OuterRef('pk'))
>>> Post.objects.annotate(count=Subquery(tags_list.count()))
最后两行应该会给出每个Post对象的标记数.在这里，我一直得到同样的错误:
ValueError: This queryset contains a reference to an outer query and may only be used in a subquery.