How can I obtain an specific message raised by a database trigger

Question

Dear friends,
if I have a database trigger and I want to show an error message which was raised from a database trigger to a form, I can do it by raising an application error inside database trigger, and by showing DBMS_ERROR_TEXT inside ON-ERROR trigger. This is ok for me.
But how can I do if I want to show a specific message? Let's say I have a BEFORE INSERT table trigger, and I want to verify whether data was correctly informed (for example, "user name must be entered"). If I raise an application error, I see a very big error message which includes both my personal error message and database message.
Surely I can do a SUBSTR in this message, but can't I do something easier? Let's say I put all error messages in a variable:
(Let's suppose it's a BEFORE INSERT trigger code, which is related to my table)
if :NEW.user_name is null then
p_error_message := 'User name must be entered.';
end if;
if p_error_message is not null then
raise_application_error (-20000, p_error_message);
end if;
... with this p_error_message being shown to final user, with no need to edit it via PL/SQL instructions like SUBSTR. Is this possible? If not, I'll be quite satisfied with SUBSTR because it fits my needs somehow.
Best regards,

Answer 1

raise_application_error will be used for raise errors on form.here i'm providing u the example
CREATE TRIGGER at AFTER UPDATE OR DELETE OR INSERT ON emp
for each row
declare
v_1 number
begin
select empno into v_1 from emp where empno=7369 ;
exception when no_data_found then
RAISE_APPLICATION_ERROR(-20001,'No data found'||sqlerrm);
END;
now when you insert data on emp table through form. if value does not found of selected empno then No data found will be shown on form
Edited by: SKYNIAZI on Mar 20, 2009 12:19 PM
Edited by: SKYNIAZI on Mar 20, 2009 12:56 PM