Named routes in mounted rails engine

The right way

I believe the best solution is to call new_post_path on the Engine’s routes proxy, which is available as a helper method. In your case, the helper method will default to basic_app_engine, so you can call basic_app_engine.new_post_path in your views or helpers.

If you want, you can set the name in one of two ways.

# in engine/lib/basic_app/engine.rb:
module BasicApp
  class Engine < ::Rails::Engine
    engine_name 'basic'
  end
end

or

# in app/config/routes.rb:
mount BasicApp::Engine => '/app', :as => 'basic'

In either case, you could then call basic.new_posts_path in your views or helpers.

Another way

Another option is to not use a mounted engine and instead have the engine add the routes directly to the app. Thoughtbot’s HighVoltage does this. I don’t love this solution because it is likely to cause namespace conflicts when you add many engines, but it does work.

# in engine/config/routes.rb
Rails.application.routes.draw do
  resources :posts, :path => '' do
                resources :post_comments
                resources :post_images
  end
end

# in app/config/routes.rb:
# (no mention of the engine)