In addition to what Aleksey replied, I noted in your CA code that you made the keyfields updatable. I would remove those from the list of updatable fields. IMHO, keys should NEVER be updated. They should be meaningless and therefore irrelevant with respect to needing to be changed.

>Mark,
>
>been thinking more about this. I understand what you're saying here, and while
>I might not need to update the left table in this case, it seems probable in
>the future.
>
>So how do I go about using a CA to create a join where only the changed record
>in the left table gets updated?
>
>Thanks