Using raise_application_error
The Package DBMS_STANDARD that is supplied with Oracle gives language facilities that help your application to interact with Oracle. For illustration, the procedure raise_application_error lets you issue user-defined error messages from the stored subprograms. In that way, you can report errors to your application and avoid returning unhandled exceptions. To call the raise_application_error, use the syntax shown below:
raise_application_error(error_number, message[, {TRUE | FALSE}]);
Where error_number is a negative integer in the range of -20000... -20999 and message is a character string of upto 2048 bytes long. When the optional third parameter is TRUE, then the error is placed on the stack of earlier errors. And If the parameter is FALSE (the default), the error replaces all earlier errors. The Package DBMS_ STANDARD is an extension of the package STANDARD, so you do not require qualifying the references to its contents.
An application can only call the raise_application_error from an executing stored subprogram (or method). Whenever called, raise_application_error ends the subprogram and returns a user-defined error number and message to the application. Error number and the message can be trapped such as any Oracle error.
In the example below, you call the raise_application_error if an employee's salary is missing:
CREATE PROCEDURE raise_salary (emp_id NUMBER, amount NUMBER) AS
curr_sal NUMBER;
BEGIN
SELECT sal INTO curr_sal FROM emp WHERE empno = emp_id;
IF curr_sal IS NULL THEN
/* Issue user-defined error message. */
raise_application_error(-20101, 'Salary is missing');
ELSE
UPDATE emp SET sal = curr_sal + amount WHERE empno = emp_id;
END IF;
END raise_salary;
The calling applications get a PL/SQL exception that can process using the error-reporting functions SQLCODE and SQLERRM in an OTHERS handler. It can also use the pragma EXCEPTION_INIT to map precise error numbers returned by the raise_application_error to exceptions of its own, as shown below:
EXEC SQL EXECUTE
/* Execute embedded PL/SQL block using host
variables my_emp_id and my_amount, which were
assigned values in the host environment. */
DECLARE
...
null_salary EXCEPTION;
/* Map error number returned by raise_application_error
to user-defined exception. */
PRAGMA EXCEPTION_INIT(null_salary, -20101);
BEGIN
...
raise_salary(:my_emp_id, :my_amount);
EXCEPTION
WHEN null_salary THEN
INSERT INTO emp_audit VALUES (:my_emp_id, ...);
...
END;
END-EXEC;
This method allows the calling application to handle error conditions in the specific exception handlers.