Here's my situation. People have Availability for Events. I need to ensure that each Person is Available for each Event exactly once.
I'm thinking the way to do it would be with a before_save method in Availability that does an
Availability.find("event_id = ? and person_id = ?", record.event_id, record.person_id)
and complains if it finds one.
Is this the way to go or is there a better approach?