Dave,
>Where do you put a check for duplicates before posting a new record?
I would put the checking in a business rule object. Business rules are checked before any transactions are started so you can bail out in a clean manner.
Regards,
Kevin McNeish
Eight-Time .NET MVP
VFP and iOS Author, Speaker & Trainer
Oak Leaf Enterprises, Inc.
Chief Architect, MM Framework
http://www.oakleafsd.com