模型協會所屬，有

Question

以下應該如何模型協會

User can purchase many Items 
Items can be purchased by many users 
Items have many categories 

Answer 1

的Active Record Associations文件似乎言自明！

你需要Item和Category之間的關係has_many和User之間Item一個has_many...through關係，。

# app/models/user.rb 
class User < ActiveRecord::Base 
    has_many :purchases 
    has_many :items, through: :purchases 
end 

# app/models/item.rb 
class Item < ActiveRecord::Base 
    has_many :purchases 
    has_many :users, through: :purchases 
    has_many :categories 
end 

# app/models/purchase.rb 
class Purchase < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :item 
end 

# app/models/category.rb 
class Category < ActiveRecord::Base 
    belongs_to :item 
end