[Zope] error catching

I'm kind novice in zope, but have learn to work around it. My postgres tables are set up with primary keys and unique index. So if there are duplicate entries it returns from postgres, a nasty error in zope if the submission was unsucessfult, that i have no idea what it is talking about ? is there a way that when the user submits data to the database via form on web site, catch the error if the user try to submit a data to the database that already exists, returned by postgres, and out put an english message saying "your data was not submited because it already exists on the database" instead of that ugly error on the zope end ? thanks to anyone if they can help.