search for: doctors_specialti

Hi, I have a scenario where a doctor can have one or more specialties. For each doctor, one and only one of her specialties can be designated as primary. So I have tables called doctors, specialties, and doctors_specialties, the last of which has a boolean is_primary column. The doctor model class specifies that: has_and_belongs_to_many :specialties I want to enforce, at the lowest possible level, the constraint that a doctor can only have one primary specialty. So, whenever a member of the association is added o...