Ruby on Rails中的多对多多态关联

Question

A Video , a Song and an Article can have many Tags . And each Tag also can have many Video, Songs or Articles . So I have 5 models: Video, Song, Article, Tag and Taggings .

Here are these models:

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

The database definition of 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 model:

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

The issue I'm worried by is, do I have right definitions of model ( belongs_to , has_many ?) ? My gut tells me that I missed something. I've seen many articles and I'm quite confused by them.

Answer 1

You need these changes:

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

About with_options .

Your class Taggings seems ok except its name . It has to be singular, Tagging :

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