Rails router constraints

app_subdomain.rb

class AppSubdomain

  def self.matches?( request )                                                                                                                                                                                                                                                                                                
    request.subdomain == 'app'
  end 

end

marketing_subdomain.rb

class MarketingSubdomain                                                                                                                                                                                                                                                                                                             

  def self.matches?( request )
    request.subdomain.blank? || request.subdomain == 'www'
  end 

end