Building Composit key on the fly, Boy Scout Data Base

Hi all,

I have two tables each is unique. One is the "Merit Badge" tabel the other
"person Id" (name address info) tabel, there is a link tabel "MB-ID_link".
This intent is to connect mert badges with the IDs of Councelors. That works
great, however, i find that i can add duplicate records (same Person, same
Merit badge many times) this is not good.

I created a "check_key" field in the Link tabel which i defined as primary
key. This will stop duplicates from being entered without a lot of code.
The problem is i am not sure how to populate the new key. I know of no way
of concatination in access or where to place the code, but it must be built
before update.

So - I tried: Check_key = trim([MB_code) & [Person_ID]) in the event calle
"before UPdate" that did not work!

It seems like such a simple thig to do!

Help

Dick