Rails 3.1质量分配层次结构

I am trying to set different access control levels (3 levels in my app) for CRUD certain model. There is no User model in the app, because I use RPAM for authentication and session for keeping track of the user. In order to set authorization levels, I created a model named user_role, to assign a role to a username. In DB, it looks like this:I am trying to set different access control lev