PL/Vision provides a set of generic routines you can use in your own programs to assert the validity of your program's assumptions. Just about every piece of software you write makes assumptions about the data it manipulates. For example, parameters may have only certain values or be within a certain range; a string value should have a certain format; an underlying data structure is assumed to have been created. It's fine to have such rules and assumptions, but it is also very important to verify or "assert" that none of the rules is being violated.
The cleanest way to perform this task is to call a prebuilt assertion routine (see Chapter 20 in Oracle PL/SQL Programming). The PLV package offers a variety of procedures to allow you to validate assumptions in the most natural possible manner. In all cases, if the assumption is violated the assertion program will take up to two actions:
Display a message if provided. This string is optional and the default for the string is NULL.
Raise the assertion_failure exception. You can then handle this exception in the program that called the assertion routine, or you can let the exception terminate that program and propagate to the enclosing block.
The PLV assertion routines come in the following flavors:
|assert||Generic assertion routine. You pass it a Boolean expression or value and assert tests to see if that expression is TRUE.|
|assert_inrange||Generic assertion routine to check date and numeric ...|