named_scope和HABTM協會

Question

我有一個模型用戶

class User < ActiveRecord::Base 
    has_many :ratings 
    has_many :rated_films, :through => :ratings, :source => :film 
end 

和電影

class Film < ActiveRecord::Base 
    has_many :users, :through => :ratings 
end 

我希望找到那些尚未被評爲由指定用戶的所有影片，不便像

class Film < ActiveRecord::Base 
    has_many :users, :through => :ratings 
    named_scope :not_rated_by_user, lambda { |user| 
    {:joins => :users, :conditions => ['? NOT IN users', user]} 
    } 
end 

Film.not_rated_by_user(User.first) 

我不熟悉SQL，所以我不太確定這是否可以在命名範圍內實現。

非常感謝

尤里

Answer 1

我假設你有一個ratings表，這是你的join表。對？所以，你需要這樣的東西：

class User < ActiveRecord::Base 
    has_many :ratings 
    has_many :rated_films, :through => :ratings, :source => :film 
end 

class Film < ActiveRecord::Base 
    has_many :ratings 
    has_many :users, :through => :ratings 

    named_scope :not_rated_by_user, lambda { |user_id| { 
     :include => :ratings, 
     :conditions => ['? NOT IN (ratings.user_id)', user_id] 
    }} 
end 

class Rating < ActiveRecord::Base 
    belongs_to :film 
    belongs_to :user 
end 

你也可以使用

Film.not_rated_by_user(User.first.id) 

請讓我知道，如果它幫助。我沒有測試！