has_many 通过自引用关联

Question

我想（作为示例）为某个人的朋友的所有帖子创建一个 has_many 关联，例如 has_many :remote_posts 给我类似 person > 的内容;朋友>人>帖子。

要采取的方法

script/generate model post title:string person_id:integer
script/generate model friendship person_id:integer friend_id:integer
script/generate model person name:string

---

class Person < ActiveRecord::Base
  has_many :posts
  has_many :friendships, :foreign_key => 'friend_id'
  has_many :people, :through => :friendships
  has_many :remote_posts, :class_name => 'Post', :through => :people, :source => :posts
end
class Friendship < ActiveRecord::Base
  belongs_to :person
  #also has a 'friend_id' to see who the friendship is aimed at
end
class Post < ActiveRecord::Base
  belongs_to :person
end

---

# generate some people and friends
{'frank' => ['bob','phil'], 'bob' => ['phil']}.each {|k,v|
  v.each {|f| 
    Friendship.create(
      :person_id => Person.find_or_create_by_name(f).id,
      :friend_id => Person.find_or_create_by_name(k).id
    )
  }
}
# generate some posts
Person.all.each {|p|
  p.posts.create({:title => "Post by #{p.name}"})
}

---

..这是我现在

Person.first.friendships  # ..works
Person.first.people  # (friends) ..works
Person.first.posts # ..works
Person.first.remote_posts #....

， ...我收到此错误..

ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: people.person_id: SELECT "posts".* FROM "posts" INNER JOIN "people" ON "posts".person_id = "people".id WHERE (("people".person_id = 1))

除了外键错误之外 - 似乎友谊关联不是'根本没有发挥作用。我在想这可能是因为 :source =>; :posts，因为 posts 关联会出现两次。

我可以编写一些 finder sql（这就是我目前正在做的事情），尽管我更愿意这样做。

关于如何让它发挥作用有什么想法吗？

Answer 1

怎么样：

在 FriendShip 类中，添加：

has_many :posts, :through => :person

并在 Person 类中，将remote_posts 更改为：

has_many :remote_posts, :class_name => 'Post',
         :through => :friendships, :source => :person

Answer 2

嵌套 has_many :through 关系怎么样。这似乎对我有用：

class Friendship < ActiveRecord::Base
  belongs_to :person
  belongs_to :friend, :class_name => 'Person'
  has_many :posts, :through => :friend, :source => :posts
end
class Person < ActiveRecord::Base
  has_many :posts
  has_many :friendships, :foreign_key => 'friend_id'
  has_many :people, :through => :friendships
  has_many :remote_posts, :through => :friendships, :source => :posts
end

注意：这需要这个 nested_has_many_through 插件。 （注意：直接链接到 github 存储库似乎已损坏......但尽管出现错误消息，该存储库仍然存在。）