时间戳

首页 > 解决方案 > 跨两个模型的 Django 简单注释

django - 跨两个模型的 Django 简单注释

问题描述

我有三个模型，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)

我想用一个“积分”列来注释用户，该列总结了他们在 UserAchievement 表中列出的所有成就所获得的总积分。

但很明显，我并没有完全了解注释的工作方式。当我尝试：

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

标签： djangoannotationsdjango-queryset

解决方案

您可以使用ManyToManyField from Userto Achievementusing UserAchievementas a through table 来简化查询

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

推荐阅读