轨道4的has_many通过

Question

我在轨道4,5下面的代码：

POST_MODEL_TO_INT = {text_post: 1, video_post: 2} 

    class Label < ActiveRecord::Base 
    end 

    module PostBase 
    include do 
     has_many :posts_to_labels, :foreign_key => :post_id, :conditions => { post_model_id: POST_MODEL_TO_INT[self.name.underscore.to_sym] } 
     has_many :labels, :through => :posts_to_labels 
    end 
    end 

    class TextPost 
    include PostBase 
    end 

    class VideoPost 
    include PostBase 
    end 

    class PostsToLabel < ActiveRecord::Base 
    belongs_to :post 
    belongs_to :label 
    end 


    TextPost.first.labels => return labels collection 

我必须添加到Label模型来获取所有从标签实例每一个职位？

Label.first.posts # -> return collection of posts Video, Text .... 
Label.first.text_posts # -> return collection of posts Text .... 

Answer 1

class Label < ActiveRecord::Base 
    has_many :posts_to_labels, :conditions => { post_model_id: 2 } 
    has_many :text_posts, :through => :posts_to_labels 
end 

class PostsToLabel < ActiveRecord::Base 
    belongs_to :post 
    belongs_to :label 
    belongs_to :text_post, :foreign_key => :post_id 
end 

我找到一个资源解决方案，但不明白为什么我需要补充的has_many到PostsToLabel？