Question

我正在尝试使用查询检查是否存在以下关系。首先，获取用户拥有的所有关注者，然后检查用户是否关注那些关注者。这是我的模特：

class Following(models.Model):
    target = models.ForeignKey('User', related_name='followers', on_delete=models.CASCADE, null=True)
    follower = models.ForeignKey('User', related_name='targets', on_delete=models.CASCADE, null=True)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return '{} is followed by {}'.format(self.target, self.follower)

class User(AbstractBaseUser):
    username    = models.CharField(max_length=15, unique=True)

    email       = models.EmailField(max_length=100, unique=True)

我正在使用Django Rest-Framework，所以我转到特定的URL以获取所需的信息。转到URL后，将得到预期的输出。我得到了用户拥有的所有关注者。

views.py

class GetFollowersView(ListAPIView):
    serializer_class = FollowingSerializer

    def get_queryset(self):
        requested_user = get_requested_user(self)
        return User.objects.filter(targets__target=requested_user).order_by('-targets__created_at'). \
            annotate(is_following=Count('followers__follower', filter=Q(followers__follower=requested_user), distinct=True))

def get_requested_user(self):
    filter_kwargs = {'username': self.kwargs['username']}
    return get_object_or_404(User.objects.all(), **filter_kwargs)

serializers.py

class FollowingSerializer(serializers.ModelSerializer):
    is_following = serializers.IntegerField()
    class Meta:
        model = User
        fields = ('id', 'username', 'follower_count', 'following_count', 'is_following')

但是，问题出在is_following批注中。我想看看用户是否关注每个特定的关注者。如果他们关注该关注者，则is_following应该为1，否则为0。我在is_following中得到不正确的结果，我可以通过这种方式检查用户是否关注每个特定的关注者？

Answer 1

如果您已安装Django Debug Toolbar，并检查查询中当前过滤器/注释的内容，则显示为（对于单个用户）

SELECT "user"."id", "user"."username", "user"."email", 
COUNT(DISTINCT T4."follower_id") AS "is_following" FROM "user" 
INNER JOIN "following" ON ( "user"."id" = "following"."follower_id" ) 
LEFT OUTER JOIN "following" T4 ON ( "user"."id" = T4."target_id" ) 
WHERE "following"."target_id" = 4 GROUP BY "user"."id", "user"."username", 
"user"."email", "following"."created_at" ORDER BY "following"."created_at" 
DESC

但是要获得所选用户所关注的用户数，您确实想要类似

SELECT ue."id", ue."username", ue."email", COUNT(DISTINCT fe."target_id") AS 
"is_following" FROM "user" u inner JOIN "following" fe ON ( u."id" = 
fe."follower_id" ) inner join user ue on fe.target_id = ue.id and u.id = 4
GROUP BY ue."id", ue."username", ue."email"

我认为不可能像您一样在同一查询中同时合并关注者和被关注者。您可能会找到路口，然后从那里开始...这样的事情。

    def get_queryset(self):
        username = self.request.query_params.get('username', None)
        requested_user = models.User.objects.get(username=username)
        following_me = models.User.objects.filter(targets__target=requested_user).order_by('-targets__created_at')
        i_follow = models.User.objects.filter(followers__follower=requested_user).order_by('-followers__created_at')
        common = following_me & i_follow
        ### Set is_following for common as 1, all others as 0.
        #......
        #......
        return following_me

Answer 2

为什么不使用M2M关系？看起来像这样简单：

from django.db import models


class User(models.Model):
    name = models.CharField(max_length=200)
    followers = models.ManyToManyField('User')

    @property
    def follower_count(self):
        # How many people follow me
        return len(self.followers)

    @property
    def followee_count(self):
        # How many people I follow
        return len(self.user_set.all())

您可以修改get_queryset()以仅找到关注者：

User.objects.filter(followers__contains=self.request.user)

有帮助吗？

检查查询是否存在关系

2 个答案: