我有三种模型，用户，成就和用户成就：

class User(AbstractUser):
    email = models.EmailField(_('email address'),unique=True)
    ...

class Achievement(models.Model):
    name = models.CharField(max_length=64)
    points = models.PositiveIntegerField(default=1)

class UserAchievement(models.Model):
    # Use a lazy reference to avoid circular import issues
    user = models.ForeignKey('users.User',on_delete=models.CASCADE)
    achievement = models.ForeignKey(Achievement,on_delete=models.CASCADE)

我想用“点数”列注释用户，该列总结了UserAchievement表中列出的所有成就所获得的总点数。

但是很明显，我并没有完全了解注释的工作方式。当我尝试时：

users = User.objects.annotate(points=Sum('userachievement__achievement__points'))
for u in users:
   print(u.email,u.points)

它崩溃与：

Traceback (most recent call last):
  File "<console>",line 1,in <module>
  File "/Users/dylan/.local/share/virtualenvs/server-E23dvZwD/lib/python3.7/site-packages/django/db/models/query.py",line 274,in __iter__
self._fetch_all()
  File "/Users/dylan/.local/share/virtualenvs/server-E23dvZwD/lib/python3.7/site-packages/django/db/models/query.py",line 1242,in _fetch_all
self._result_cache = list(self._iterable_class(self))
  File "/Users/dylan/.local/share/virtualenvs/server-E23dvZwD/lib/python3.7/site-packages/django/db/models/query.py",line 78,in __iter__
setattr(obj,attr_name,row[col_pos])
AttributeError: can't set attribute