Should I check for DB constraints in code or should I catch exceptions thrown by DB

Question

I have an application that saves data into a table called Jobs. The Jobs table has a column called Name which has a UNIQUE constraint. The Name column is not PRIMARY KEY. I wond

Answer 1

If your design is good (both database and BL), the database shouldn't have any constraints that wouldn't be dealt with in the BL - i.e. you shouldn't be presenting the database with inconsistent data. But nothing is perfect.

I've found that confining the database to data consistency constraints lets me handle all BL validation in procedural code, and the only cases where I experience database exceptions are design and coding errors which can (and should be) fixed.

In your case, checking the name for uniqueness is data content validation, properly handled in code. Which presumably catches the error nearest the point of commission, where you hopefully have friendlier UI resources to call on without introducing undesirable coupling between abstractions.