跨两个模型的 Django 简单注释

Question

我有三个模型，User、Achievement 和 UserAchievement：

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)

我想用一个 'points' 列来注释用户，该列总结了他们在 UserAchievement table 中列出的所有成就所获得的总分。

但显然我还没有完全了解注释的工作原理。当我尝试时：

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

它崩溃了：

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

Answer 1

您可以使用 ManyToManyField 从 User 到 Achievement，使用 UserAchievement 作为直通 table 来简化您的查询

class User(AbstractUser):
    email = models.EmailField(_('email address'), unique=True)
    achievements = models.ManyToManyField('Achievement', through='UserAchievement')
    ...

这可以像这样用于注释

User.objects.annotate(points=Sum('achievements__points'))

如果你有一个用户实例

user.achievements.all()

至于错误，我相信您的用户模型上有一个名为 points

的属性

跨两个模型的 Django 简单注释

Django simple annotation across two models

django

annotations

django-queryset