New to Ruby on Rails - model/migration clarification?

New to Ruby on Rails - model/migration clarification?

Sorry for the basic, basic question but I'm having some trouble understanding the RoR doc. say I have 3 models--Students, Classes, and Enrolled_in. If it isn't clear, students will enroll in classes, so Enrolled_in should have Students and Classes as foreign keys. I generated the models for each of these, but I'm confused what I should put into the associated migration file vs. the associated model file for each table. Do I specify the columns of the table in the migration file, and the key constraints in models? If someone could clarify this, or tell me how they would solve the example question I posted, that would be really helpful. Thanks.

Full article: http://stackoverflow.com/questions/12658015/new-to-ruby-o...