Oracle PL/SQL Programming, 5th Edition

Chapter 6. Exception Handlers

It is a sad fact of life that many programmers rarely take the time to properly bullet-proof their programs. Instead, wishful thinking often reigns. Most of us find it hard enough—and more than enough work—to simply write the code that implements the positive aspects of an application: maintaining customers, generating invoices, and so on. It is devilishly difficult, from both a psychological standpoint and a resources perspective, to focus on the negative: for example, what happens when the user presses the wrong key? If the database is unavailable, what should I do?

As a result, we write applications that assume the best of all possible worlds, hoping that our programs are bug-free, that users will enter the correct data in the correct fashion, and that all systems (hardware and software) will always be a “go.”

Of course, harsh reality dictates that no matter how hard you try, there will always be one more bug in your application. And your users will somehow always find just the right sequence of keystrokes to make a form implode. The challenge is clear: either you spend the time up-front to properly debug and bulletproof your programs, or you fight an unending series of rear-guard battles, taking frantic calls from your users and putting out the fires.

You know what you should do. Fortunately, PL/SQL offers a powerful and flexible way to trap and handle errors. It is entirely feasible within the PL/SQL language to build an application that fully protects ...