Accessing Rails engine's URL helpers in initializer

Question

I'm trying to access the url helpers in my engine to set up rack-cors. Right now, I've hard-coded the strings for one of the urls in the rack-cors middleware configuration. I have read the order in which Rails initializers are run, and at this point in the load order I should have the engine routes available to me. I thought I would have them available at the event add_routing_paths, but I couldn't find the routes after digging around using pry. Another statement that leads me to think I'm doing this incorrectly is that the docs say: "Some parts of your application, notably routing, are not yet set up at the point where the after_initialize block is called." According to this list:

1. require "config/boot.rb" to setup load paths
2. require railties and engines
3. Define Rails.application as "class MyApp::Application < Rails::Application"
4. Run config.before_configuration callbacks
5. Load config/environments/ENV.rb
6. Run config.before_initialize callbacks
7. Run Railtie#initializer defined by railties, engines and application. One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.
8. Custom Railtie#initializers added by railties, engines and applications are executed
9. Build the middleware stack and run to_prepare callbacks
10. Run config.before_eager_load and eager_load! if eager_load is true
11. Run config.after_initialize callbacks

I'm trying to hook into (7), but perhaps routes aren't available until (11)?

module Zillow
  class Engine < ::Rails::Engine
    isolate_namespace Zillow

    # Rails.application.routes.url_helpers

    initializer "zillow.cors", after: :set_routes_reloader do |app|
      require 'pry'; binding.pry
      app.config.app_middleware.insert_before 0, Rack::Cors do
        allow do
          origins 'localhost:3000'
          resource '/zillow/search_results', methods: :get
        end
      end
    end
  end
end

Here is the output of my routes

zillow  /zillow Zillow::Engine

Routes for Zillow::Engine:
              api_deep_comps GET /api/deep_comps(.:format)               zillow/api#deep_comps
               api_zestimate GET /api/zestimate(.:format)                zillow/api#zestimate
          api_search_results GET /api/search_results(.:format)           zillow/api#search_results
api_updated_property_details GET /api/updated_property_details(.:format) zillow/api#updated_property_details

Answer 1

Load it just after initialize.

I needed to use root_url in my initializer but it wasn't properly initialized. I tried using the Pub / Sub method that Anton Styagun suggests but even when that's called the URL Helpers were not properly initialized.

Instead, I opted to load my initializer file manually just after the Rails app itself has initialized. This takes a few steps:

1. Move your initializer from config/initializers/ to lib/.

2. Require your file in environment.rb just after your application initializes. Ours looks something like this:

   CNTRAL::Application.initialize!
   
   require "my_initializer" # Omit the `lib/` because that's the load path it looks in.
   

3. Now, inside of my_initializer.rb I was able to call root_url by doing this:

   Rails.application.routes.url_helpers.root_url
   

   NOTE: It's important not to just use include Rails.application.routes.url_helpers. It raised an exception on me.

I also added a comment in both the initializer and the environment.rb of where this was loaded/required so it's more obvious to myself in the future and other engineers.

Alternative Method

You can also use the following method and it works well:

In your application.rb file, add:

config.after_initialize do
  Rails.application.reload_routes! # Necessary to load the Routes.
  require  "my_initializer"
end

Answer 2

You can fire your own event when routes are loaded and then subscribe to that event during initialization to get routes data. For that:

1. Add this to the end of config/routes.rb file (outside of routes.draw block)

ActiveSupport::Notifications.instrument 'routes_loaded.application'

2. Subscribe to this event in initialization code and use URL helpers!

ActiveSupport::Notifications.subscribe 'routes_loaded.application' do
  Rails.logger.info Rails.application.routes.url_helpers.home_path
end

For more information see:

• Subscribing to an event
• Creating custom events

Answer 3

After looking into this further and reading the rack-cors example done in Rails3, it may not be possible to retrieve the route helpers inside the initializer at any point in time.