双向自引用关联

Question

以Ryan Bates的asciicast为例:http://asciicasts.com/episodes/163-self-referential-association

他以两个User用户结束

• :朋友
• :inverse_friends

鉴于用户不关心是谁煽动友谊,你会想要一个简单的用户关联

• :朋友

这包括两种关系.即,由用户发起的关系和由用户的朋友发起的关系.

那么如何实现这种双向自引用关联呢？

更新 - Josh Susser在此发表了一篇文章:http: //blog.hasmanythrough.com/2006/4/21/self-referential-through

但是,它仍然讨论has_many:sources和has_many:当真的应该有一个has_many:包含源和接收器的节点时接收.

Answer 1

看看这对你有用吗？

class User < ActiveRecord::Base
  has_many :friendships, :foreign_key => "person_id", :class_name => "Friendship"
  has_many :friends, :through => :friendships

  def befriend(user)
    # TODO: put in check that association does not exist
    self.friends << user
    user.friends << self
  end
end

class Friendship < ActiveRecord::Base
  belongs_to :person, :foreign_key => "person_id", :class_name => "User"
  belongs_to :friend, :foreign_key => "friend_id", :class_name => "User"  
end

# Usage
jack = User.find_by_first_name("Jack")
jill = User.find_by_first_name("Jill")

jack.befriend(jill)

jack.friends.each do |friend|
  puts friend.first_name
end
# => Jill

jill.friends.each do |friend|
  puts friend.first_name
end
# => Jack

这是给出了一个数据库表模式

users
  - id
  - first_name
  - etc...

friendships
  - id
  - person_id
  - friend_id