A Guide to Active Record Associations

@sanjay see 4.2.2.6 to set the foreign keys so that Rails knows what to do:

is a connection between two Active Record models. Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model belongs_to another, you instruct Rails to maintain Primary Key–Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model. Rails supports six types of association:

Full article: http://guides.rubyonrails.org/v2.3.11/association_basics....