如何为current_user.following创建作用域？

Question

这里是我的用户和关系模型

class User < ActiveRecord::Base 
    has_many :active_relationships, class_name: "Relationship", 
           foreign_key: "follower_id", 
           dependent: :destroy 
    has_many :passive_relationships, class_name: "Relationship", 
           foreign_key: "followed_id", 
           dependent: :destroy 
    has_many :followers, through: passive_relationships, source: :follower 
    has_many :following, through: :active_relationships, source: :followed 

class Relationship < ActiveRecord::Base 
    belongs_to :follower, class_name: "User", counter_cache: :followeds_count 
    belongs_to :followed, class_name: "User", counter_cache: :followers_count 
    validates :follower_id, presence: true 
    validates :followed_id, presence: true 
    validates :followed, uniqueness: { scope: [:follower, :followed] } 
end 

在用户控制器我可以这样做：

@users = current_user.following 

不过，我想这变成我的用户模型中的范围。

Answer 1

有两件事情你可能接近：

1. 找到所有正在关注某人的用户

   class User < ActiveRecord::Base 
       scope :following_to, -> (user_id) { 
       where(
        "id IN (SELECT followed_id 
          FROM relationships 
          WHERE follower_id = ? 
         )", 
        user_id 
       ) 
       } 
   end 
   

2. 查找谁是下任何人的所有用户，这意味着他们是跟随

   class User < ActiveRecord::Base 
       scope :follower, -> { 
       where("id IN (SELECT followed_id FROM relationships)") 
       } 
   end 
   

最后，您可以使用这些范围，因为你的期望：

# Find all users who are following to User (id = 1) 
User.following_to(1) 

# Find all users who are following someone, 
# aka they are a follower 
User.follower 

Answer 2

通过使用实例方法可以使一个方法对于用户模型

这样的：

class User < ActiveRecord::Base 

    def following? 
    self.following.present? 
    end 

end 

使用范围则只能拨打ActiveRecord的基于查询到模型的范围。

Answer 3

你也应该得到这样

scope :following?, lambda { |user| 
    { user.following.present? } 

，这应该在你的控制器来调用诸如

User.following?(current_user)