In Rails, "models" represent data (like a User or an Order), how they are saved to the database, and how they behave. "Controllers" coordinate pulling the correct models out of the database when they need to be rendered to HTML or other request. The longstanding conventional wisdom regarding the two is "fat model, skinny controller"; i.e., if you have complicated logic about for example which User can view which Orders, don't put that logic where you generate the page, but move it into the User object.
The problem is that eventually you get very fat models. You can easily imagine how much behavior something as common as a User might have, and you get massive classes that act like junk drawers for can_view_order? and can_order_new_item? and has_archived_orders? etc. DHH here is presenting a possible solution to that problem. There are links elsewhere here to other solutions.
The problem is that eventually you get very fat models. You can easily imagine how much behavior something as common as a User might have, and you get massive classes that act like junk drawers for can_view_order? and can_order_new_item? and has_archived_orders? etc. DHH here is presenting a possible solution to that problem. There are links elsewhere here to other solutions.