You don't have to avoid such constraints if they are natural to data model actually. It's much faster (and safer, thanks to transactions) to check new data agai

You don't have to avoid such constraints if they are natural to data model actually. It's much faster (and safer, thanks to transactions) to check new data against some old data when the checking code is as close to the data as possible, instead of make a couple additional requests between DBMS and the business logic layer.