Unique value per id not whole table

I have a form to save contacts and each contact can have multiple contact info for instance, a primary and then mailing, other etc. I want to set up a server side validation so that if more than one contact info entry is marked as ‘Primary’ then submitting the form fails.

Screen Shot 2021-02-19 at 9.30.48 AM244×754 10.7 KB

Is this possible using the ‘unique’ validator in Wappler and if so how do you use it per id? If not possible, can I write my own validator and is there documentation on how to do so?

Thanks in advance.