Map a scoped resource to a controller with an unrelated namespace

routes.rb

Sample::Application.routes.draw do
  # Route /a/b -> Foo::BarsController.  This is useful
  # when you need to conform to a certain url structure
  # while using a controller that doesn't match that structure,
  # eg. a controller supplied by a Rails engine.
  scope '/a' do
    resources :b, controller: 'bars', module: 'foo'
  end
end