has_many：通过外键？

Question

我已经阅读了多个关于此的问题，但尚未找到适合我情况的答案。

我有 3 个模型：Apps、AppsGenres 和 Genres

以下是每个字段的相关字段：

Apps
application_id

AppsGenres
genre_id
application_id

Genres
genre_id

这里的关键是我不使用这些模型中的 id 字段。

我需要根据application_id 和genre_id 字段关联表。

这是我目前得到的，但没有得到我需要的查询：

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

作为参考，这是我最终需要的查询：

@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

更新试试这个：

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

有查询：

App.find(1).genres

它生成：

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

并查询：

Genre.find(1).apps

生成：

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