has_many：通過一個外鍵？

Question

我已閱讀過關於此的多個問題，但尚未找到適用於我的情況的答案。

我有3種型號：Apps，AppsGenres和Genres

下面是每個的人的相關字段：

Apps 
application_id 

AppsGenres 
genre_id 
application_id 

Genres 
genre_id 

這裏的關鍵是，我使用id場不來自這些模型。

我需要根據那些application_id和genre_id字段關聯表格。

這裏就是我目前得到的，但它沒有得到我，我需要查詢：

class Genre < ActiveRecord::Base 
    has_many :apps_genres, :primary_key => :application_id, :foreign_key => :application_id 
    has_many :apps, :through => :apps_genres 
end 

class AppsGenre < ActiveRecord::Base 
    belongs_to :app, :foreign_key => :application_id 
    belongs_to :genre, :foreign_key => :application_id, :primary_key => :application_id 
end 

class App < ActiveRecord::Base 
    has_many :apps_genres, :foreign_key => :application_id, :primary_key => :application_id 
    has_many :genres, :through => :apps_genres 
end 

以供參考，在這裏是查詢我最終需要：

@apps = Genre.find_by_genre_id(6000).apps 

SELECT "apps".* FROM "apps" 
    INNER JOIN "apps_genres" 
     ON "apps"."application_id" = "apps_genres"."application_id" 
    WHERE "apps_genres"."genre_id" = 6000 

Answer 1

修訂試試這個：

class App < ActiveRecord::Base 
    has_many :apps_genres, :foreign_key => :application_id 
    has_many :genres, :through => :apps_genres 
end 

class AppsGenre < ActiveRecord::Base 
    belongs_to :genre, :foreign_key => :genre_id, :primary_key => :genre_id 
    belongs_to :app, :foreign_key => :application_id, :primary_key => :application_id 
end 

class Genre < ActiveRecord::Base 
    has_many :apps_genres, :foreign_key => :genre_id 
    has_many :apps, :through => :apps_genres 
end 

隨着查詢：

App.find(1).genres 

它產生：

SELECT `genres`.* FROM `genres` INNER JOIN `apps_genres` ON `genres`.`genre_id` = `apps_genres`.`genre_id` WHERE `apps_genres`.`application_id` = 1 

和查詢：

Genre.find(1).apps 

產生：

SELECT `apps`.* FROM `apps` INNER JOIN `apps_genres` ON `apps`.`application_id` = `apps_genres`.`application_id` WHERE `apps_genres`.`genre_id` = 1