Grape でファイル分ける

grape.rb

# app/api/users.rb
class Users < Grape::API
  format :json

  get do
    # returns users
  end

  get ':id' do
    # returns user
  end

  # nested resources
  route_param :user_id do
    mount Users::Books
  end
end

# app/api/users/books.rb
class Users::Books < Grape::API
  resource :books do
    get do
      # return user books
    end

    get ':id' do
      # return user book
    end
  end
end

# config/routes.rb
SomeApp::Application.routes.draw do
  mount Users => '/api/users'
end

# config/application.rb
module SomeApp
  class Application < Rails::Application
    config.autoload_paths += %W(#{config.root}/app/api)
  end
end

$ curl some_app/api/users
[{"id":1,"name":"user1"},{"id":2,"name":"user2"}]

$ curl some_app/api/users/1
{"id":"1","name":"user1"}

$ curl some_app/api/users/1/books
[{"id":1,"name":"user1_book1"},{"id":2,"name":"user1_book2"}]

$ curl some_app/api/users/1/books/1
{"id":"1","name":"user1_book1"}