How to setup a association through multiple models

Question

I've the followig three models in Rails:

class Book < ActiveRecord::Base
    has_many :chapters
    has_many :pages
end

class Chapter < ActiveRecord::Base
    belongs_to :book
    has_many :pages
end

class Page < ActiveRecord::Base
    belongs_to :chapter
end

How is it possible do to a query like: Book.first.pages.count to get the number of pages of the whole book. By now I dont even know if i set my model up the right way. Would be great if you could help me out here.

Thanks in advance!

Answer 1

You can use a has_many through relationship as outlined here

class Book < ActiveRecord::Base
    has_many :chapters
    has_many :pages, through: :chapters
end

class Chapter < ActiveRecord::Base
    belongs_to :book
    has_many :pages
end

class Page < ActiveRecord::Base
    belongs_to :chapter
end

That enables you to do book.pages.count