[Rails] pathから値を読んでテンプレートを分岐させる

Routes

namespace 'manage' do
  get 'dashboard/:first_nav/:second_nav/:redirect_to', :controller => "dashboard", :action => "index", :as => "dashboed"
  get 'dashboard/:first_nav/(:second_nav)', :controller => "dashboard", :action => "index", :as => "dashboard"
end

Controller

class Manage::DashboardController < ManageController
  def index
    if params[:second_nav].blank?
      render :action => "#{params[:first_nav]}"
    elsif params[:redirect_to].blank?
      render :action => "#{params[:first_nav]}_#{params[:second_nav]}"
    else
      redirect_to "/manage/#{params[:redirect_to]}"
    end
  end
end