ActiveRecord, like all ORM’s, is one of the greatest things on earth, IMHO
By using the Convention or Configuration approach, ActiveRecord and even Rails, allows you to skip a few parts and go straight to what matters: the development.
sometimes, though, the “Sensible defaults” of rails and ActiveRecord are’t enough, but like most ORM’s, the convention can easily be overridden in order to get things done.
When you add a relationship between classes all you have to do is to add a references and has_many on the other side. If you follow the naming rules everything works.