Hi Thea...I might be missing something here, but in the portal setup dialog, you have the option to sort portal records. You could sort the portal by the date of the response, assuming that responses is a portal on the invitations layout.
If you can set up a self join by respondant ID, you can filter out all but the records with the most recent reponses:
Event::__pkEventID = Responses::_fkEventID
Responses::_fkRespondantID = ResponsesByRespondantID::_fkRespondantID AND
Responses::_fkEventID = ResponsesByRespondantID::_fkEventID
Both Responses and ResponsesByRespondantID would be occurrences of the same table.
Then define this calculation field, cMostRecent in Responses, set to evaluate from the context of Responses:
Max ( ResponsesByRespondantID::DateResponded ) //select "Date" as the return type
Now you can use this portal filter for a portal to Responses to filter out all but the most recent responses by each respondant:
Responses::cMostRecent = Responses::DateResponded
Awesome, thanks Phil! That worked perfectly. :-)
Thanks also Chris - sorting by the date and respondant name would show all responses by all people, but ideally I wanted to not display the out-of-date responses in the portal when people change their minds, which Phil's answer solves. This way, the Responses table has the complete history of what we have been told if we need to refer back to it, and the portal just gives us the current info per person.