双向自引用关联 [英] Bidirectional self referential associations

问题描述

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

Taking Ryan Bates' asciicast as an example: http://asciicasts.com/episodes/163-self-referential-association

他以两个用户关联结束

• :朋友
• :inverse_friends

鉴于用户不关心谁促成了友谊，您需要一个简单的用户关联

Given that a user would not care who instigated the friendship, you would want a User association that was simply

• :朋友

由两种关系组成.即用户发起的关系和用户朋友发起的关系.

that consisted of both relationships. i.e Relationships instigated by the user and relationships instigated by the user's friend.

那么如何实现这种双向自引用关联?

So how can you achieve this bidirectional self-referential association?

更新 - Josh Susser 在这里发表了一篇关于此的帖子:http://blog.hasmanythrough.com/2006/4/21/自我参照

UPDATE - Josh Susser has a post about this here: http://blog.hasmanythrough.com/2006/4/21/self-referential-through

然而，它仍然谈论 has_many :sources 和 has_many :sinks，而实际上应该有一个包含源和接收器的 has_many :nodes.

However, it still talks about has_many :sources and has_many :sinks when really there should be a has_many :nodes that includes both the sources and the sinks.

推荐答案

看看这是否适合您?

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

这是给定的数据库表模式

this is given a database table schema of

users
  - id
  - first_name
  - etc...

friendships
  - id
  - person_id
  - friend_id

这篇关于双向自引用关联的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！