This is a sample problem to see how ROM might be used in a (relatively) real world situation. I've encountered projects where the database is controlled by a DBA and so developers had to basically treat it as a 3rd party api.
Check the master branch for the feature test that asserts the app's api behavior. To see the flattened (ugly) implementation
in the controller to see a basic implementation using ActiveRecord.
Check the rails-way branch for how a more optimal ActiveRecord implementation.