has_many :through with a foreign key?

Question

I've read multiple questions about this, but have yet to find an answer that works for my situation.

I have 3 models: Apps, AppsGenres and Genres

Here are the pertinent fields from each of those:

Apps application_id  AppsGenres genre_id application_id  Genres genre_id 

The key here is that I'm not using the id field from those models.

I need to associate the tables based on those application_id and genre_id fields.

Here's what I've currently got, but it's not getting me the query I need:

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 

For reference, here is the query I ultimately need:

@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

UPDATED Try this:

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 

With query:

App.find(1).genres 

It generates:

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

And query:

Genre.find(1).apps 

generates:

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