I have a custom object (visit) that is child record of another object(patient). The relationship is one to many, one patient can have many visits. Visit object has multiple record types.
I would like to prohibit duplicate visit types for any one patient. So each patient could have a preop, 1 month and 3 month visit. But I would like to stop a patient from having 2 preop visit types.

 

So the rule would look to see if there are any visit records pre-existing that already contain the master-detail value (this would reference the parent object) and new record type. I think that is the simplest way, but tell me if I am off base

 

thanks for any help