Ruby on Rails中的多对多关联

Question

A Video，Song和Article可以有许多Tags。而且每个Tag也可以有很多Video, Songs or Articles。所以我有5个型号：Video, Song, Article, Tag and Taggings。

下面是这些模型：

class Video < ActiveRecord::Base 
    has_many :tags, :through => :taggings 
end 

class Song < ActiveRecord::Base 
    has_many :tags, :through => :taggings 
end 

class Article < ActiveRecord::Base 
    has_many :tags, :through => :taggings 
end 

class Tag < ActiveRecord::Base 
    has_many :articles 
    has_many :videos 
    has_many :songs 
    belong_to :taggings, :polymorphic => true #is this correct? 
end 

的数据库定义Taggings

create_table "taggings", :force => true do |t| 
    t.integer "tag_id" 
    t.string "taggable_type" 
    t.integer "taggable_id" 
    t.datetime "created_at", :null => false 
    t.datetime "updated_at", :null => false 
end 

Taggings型号：

class Taggings < ActiveRecord::Base 
    belongs_to :tag       #is this correct? 
    belong_to :taggable, :polymorphic => true #is this correct? 
end 

我担心的是这个问题，我有模型的正确定义（belongs_to,has_many？）？我的直觉告诉我，我错过了一些东西。我看过很多文章，我很困惑。

Answer 1

您需要这些变化：

class Video < ActiveRecord::Base # or Song, or Article 
    has_many :taggings, :as => :taggable # add this  
    has_many :tags, :through => :taggings # ok 


class Tag < ActiveRecord::Base 
    # WRONG! Tag has no tagging_id 
    # belong_to :taggings, :polymorphic => true 

    has_many :taggings # make it this way 

    # WRONG! Articles are available through taggings 
    # has_many :articles 

    # make it this way 
    with_options :through => :taggings, :source => :taggable do |tag| 
    tag.has_many :articles, :source_type => 'Article' 
    # same for videos 
    # and for songs 
    end 

关于with_options。

您的类Taggings好像除了它的名字。它必须是单数，Tagging：

class Tagging < ActiveRecord::Base # no 's'! 
    belongs_to :tag       
    belong_to :taggable, :polymorphic => true 
end