So http://guides.rubyonrails.org/migrations.html, states that: "The Active Record way claims that intelligence belongs in your models, not in the database. As such, features such as triggers or foreign key constraints, which push some of that intelligence back into the database, are not heavily used." (8 Active Record and Referential Integrity)

I'm just going to set up the relationships in the code for now and not worry about the proper FK in the db at the moment.  We can revisit later.