Allowing only 1 checkbox with related records

[scoony]

Hi!

 

I have a client database with two tables: Client, Contacts. Each client can have many contacts attributed to it but each client can have only 1 'Key Contact' which I would like to show in a list format based upon the Client table.  What I have tried to create is a simple check box on the new contact layout to highlight which contact is the key contact and then be able to show that key contact field on the client list layout. 

 

As a newbie I can't determine if this requires a search, a validation to ensure no two related contacts have the 'key contact' field checked, or something along the lines of a if calculation. 

 

Any help would be much appreciated.

 

Thanks!

 

 

[eos]

Preferably, do this the other way around: instead of giving a contact the attribute of 'being a key contact for a client', give the client the attribute of 'having the ID of a key contact'. This means you'll store a key contact's ID with the client, so you simply cannot store more than one key contact.

 

See the attached sample file.

KeyContact_eos.fmp12.zip