Best way to manage exception in package - oracle

Question

I have a package with a several procedures and functions, the procedures are called from an external program and in turn they call functions.
Where is the best way to manage a Exception?
For example, Prog1 call Proc1 and Proc1 call the Funct1, if in function I have an exception ("TOO MANY ROW" or "NO DATA FOUND"), which is the best way to raise a specific customized message and return immediatally to Prog1.
In this moment I have this
PROCEDURE_1
BEGIN
*code*
CALL FUNCTION_1
*code*
EXCEPTION
WHEN NO DATA FOUND THEN
*print customized message*
RETURN;
END;
FUNCTION_1
BEGIN
*code*
EXCEPTION
WHEN NO DATA FOUND THEN
RAISE;
END;
It is the best way?
Regards,
Marco

Answer 1

Ideally a procedure would be allowed to fail with an exception and error stack if something went totally wrong, but then the difference between a fatal error and an expected condition will vary depending on the business logic you are implementing, so it's hard to say what should happen in your particular case.
If the agreed interface is that the procedure should return a formatted message, and that message may include expected business conditions such as a product being out of stock, then you can handle that within the procedure using something like this (nonsense pseudocode to illustrate approach only):
create or replace procedure procedure_1
( p_result_message out varchar2 )
as
somevar number;
begin
do_stuff('fruit','cake');
begin
somevar := function_1('bananas');
exception
when no_data_found then
p_result_message := 'No kittens are available for this mission.';
return;
end;
p_result_message := 'Cake is available in aisle 3';
exception
when something_else then
p_result_message := 'Self-destruct sequence initiated.';
end;
(For a more purist approach you might prefer to rearrange the code so that it always reaches the end with a value for p_result_message, rather than quitting partway through if some condition pops up.)
Now you have a way to handle whatever exceptions might reasonably arise in function_1, without any special handling within the function itself.
You could also have the function raise an exception defined in a package, although then you lose the ability to define a diagnostic error message at the point of failure, and in my experience this just tends to complicate things. But to illustrate:
create or replace package starfleet
as
shield_failure exception;
warp_core_malfunction exception;
pragma exception_init(shield_failure, -20998);
pragma exception_init(warp_core_malfunction, -20999);
procedure check_status
( status_message out varchar2 );
function status
return number;
end starfleet;
create or replace package body starfleet as
function status
return number
is
status_ind number;
begin
select 1 into status_ind from dual where 1=2; -- fails with NDF
return status_ind;
exception
when no_data_found then raise shield_failure;
end status;
procedure check_status
( status_message out varchar2 )
is
status_ind number;
begin
status_ind := status();
status_message := 'Everything is fine';
exception
when warp_core_malfunction then status_message := 'Abandon ship';
when shield_failure then status_message := 'Increase power to shields';
end check_status;
end starfleet;
Now, the status() function can raise exceptions defined in the package (or any other package for that matter), and procedure check_status can catch it and decide how to handle it.
Example of calling it from SQL*Plus:
SQL> var status_message varchar2(100)
SQL>
SQL> begin
2 starfleet.check_status(:status_message);
3 end;
4 /
PL/SQL procedure successfully completed.
STATUS_MESSAGE
-------------------------
Increase power to shields