routes_with_slugs.rb

# config/initializers/routes_with_slugs.rb
require 'action_dispatch'

module ActionDispatch
  module Routing
    class Mapper
      module Resources
        RESOURCE_OPTIONS << :slug
        
        class Resource
          def member_scope_with_slug
            if @options[:slug]
              "#{path}/:id(/:slug)"
            else
              member_scope_without_slug
            end
          end
          
          alias_method_chain :member_scope, :slug
        end
      end
    end
  end
end