为什么在进行能力检查时没有显示数据？（rails，cancancan）

I want 3 user levels as Admin ,Manager,Customer in my rails application. So i've created a devise model as Users and added a migration to add the user role to it.So when a user is signed up it stores the users role(whether he is an admin,a manager or a customer). And in my application there are models and controllers for product,delivery,services. And I want to set access levels to each models.I want 3 user levels as Admin ,Manager,Customer