本人是一个新手，最近尝试使用 cancancan 做权限等级设置，代码写完后，在本地运行通过了，但是部署到服务器上面之后，项目不能正常运行，查看 log 的时候发现提示这个错误，undefined local variable or method `authorize_resource' for AdminController:Class (NameError)，请求大神帮帮忙。

class AdminController < ApplicationController
   authorize_resource
   rescue_from CanCan::AccessDenied do |exception|
     if request.env["HTTP_REFERER"] == nil
       redirect_to admin_activities_path, :alert => exception.message
     else
       redirect_to request.env["HTTP_REFERER"], :alert => exception.message
     end
   end
   def current_ability
      @current_ability = Ability.new(current_user)
   end
end

class Ability
   include CanCan::Ability

   def initialize(user)
      if user.username == "admin"
          can :manage, :all
      else
          can :manage, Activity
      end
   end
end