Question

我想（作为示例）为一个人的朋友创建一个has_many关联给所有帖子，类似于has_many :remote_posts给我一些person > friends > person > posts。

..这就是我要怎么做的

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}"})
}

现在，

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

......我收到了这个错误..

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 - 似乎友谊协会根本没有发挥作用。我认为这可能是因为:source => :posts，因为posts关联会进入两次。

我可以写一些finder sql（这就是我现在正在工作的东西），虽然我很快就会这样做。

有关如何使其发挥作用的任何想法？

Answer 1

这个怎么样：

在FriendShip课程中，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：这需要此nested_has_many_through plugin。（注意：直接链接到github repos似乎被打破了......但是尽管出现了错误信息，那个回购仍然存在。）

has_many通过自我参照联想

2 个答案: