如何在Django视图中基于外键过滤模型数据？

Question

我有两个模型，分别是User和UserRating，它们之间是一对多的关系，如何过滤特定用户的评分，以便可以计算出其总体评分并将其显示在个人资料中。 谢谢。

#this is model for user
class User(models.Model):
    username = models.CharField(max_length=128, unique=True)
    email = models.EmailField(max_length=128, unique=True)
    #password = forms.CharField(max_length=32, widget=forms.PasswordInput)
    profilepic = models.ImageField(null=True)
    firstname = models.CharField(max_length=128, null=True)
    secondname = models.CharField(max_length=128, null=True)
    city = models.ForeignKey(City)


#this is the model for user ratings - one to many relationship with User
class UserRating(models.Model):
    user = models.ForeignKey(User)
    comment = models.CharField(max_length=500)
    rating = models.IntegerField(default=5)

Answer 1

如果您有一个User对象，则可以通过反向关系访问其所有评分：

user.userrating_set.all()

要计算他的平均评分，请使用Aggregation

from django.db.models import Avg
user.userrating_set.all().aggregate(Avg('rating'))

编辑

如果要将其作为用户模型的属性，请执行以下操作：

class User(models.Model):
    username = models.CharField(max_length=128, unique=True)
    ... 

    @property
    def avg_rating(self):
        return self.userrating_set.all().aggregate(Avg('rating'))

然后您可以使用

user.avg_rating

Answer 2

编辑 -已更新，因此您可以除以评分数

在视图中...

from django.db.models import Sum

current_user_rating_object = UserRating.objects.filter(user=request.user)
ratings = current_user_rating_objects.count()
total_rating = current_user_rating_object.aggregate(Sum(total_rating=Sum('rating', distinct=True))['total_rating']
weighted_rating = total_rating / ratings