Url helper with constraints for a subdomain rails app

Question

My rails app have two servers and the urls are:

• staging.subdomain.example.com
• subdomain.example.com

And my routes look like:

  ['staging.', ''].each do |prefix|
    constraints subdomain: "#{prefix}subdomain" do
      scope module: "subdomain" do
        get "/", to: "pages#home"
        resources :courses, only: [:index, :show]
      end
    end
  end

However, when I uses the url helpers, I meet a problem. It always returns the staging url.

For example, on production:

course_url(132, host: "subdomain.example.com")
=> "http://staging.subdomain.example.com/courses/132"

I think the reason is that in the routes, the url helpers are only generated for staging constraint, not the other one.

$ rate routes
...
courses GET  /courses(.:format)  subdomain/courses#index {:subdomain=>"staging.subdomain"}
        GET  /courses(.:format)  subdomain/courses#index {:subdomain=>"subdomain"}
...

Does anyone have a good solution?

Cheers