How to use dynamic alerts for login form? - oracle

Question

I am new at Oracle development using oracle 10g Forms.
I am trying to write this code for login purpose. When user enters wrong password, it gives alert in popup window. Also, when user enters wrong username, it raise an alert.
I wrote this code but I am unable to correct it.
DECLARE
un VARCHAR (15);
pwd VARCHAR (15);
BEGIN
--- Dynamic altert properties code start--
SET_ALERT_PROPERTY ('LOGIN_ALERTS', TITLE, 'Security Altert');
SET_ALERT_PROPERTY ('LOGIN_ALERTS',
ALERT_MESSAGE_TEXT,
'Wrong Username?');
SET_ALERT_PROPERTY ('LOGIN_ALERTS',
ALERT_MESSAGE_TEXT,
'Wrong Password?');
SELECT username, users_password
INTO un, pwd
FROM MENU_USERS
WHERE username = :TXT_USERNAME;
IF un = :TXT_USERNAME
THEN
IF pwd = :TXT_PWD
THEN
CALL_FORM ('F:\ISMS\INV\inv_stock.fmx');
ELSE
SHOW_ALERT ('LOGIN_ALERTS');
END IF;
ELSE
SHOW_ALERT ('LOGIN_ALERTS');
END IF;
END;

Answer 1

Alerts are OK, but - consecutive message calls will do as well. This example shows how to use that approach.
Code you wrote is kind of "wrong" as it doesn't handle "wrong username" situation. When that happens, select won't return anything and will raise the no_data_found exception which should be handled.
Here you go:
declare
pwd varchar2(15);
begin
select users_password
into pwd
from menu_users
where username = :txt_username;
-- if TXT_USERNAME value exists, SELECT will return its password
if pwd = :txt_pwd then
call_form('whichever form you want');
else
message('Wrong password');
message('Wrong password');
raise form_trigger_failure;
end if;
exception
when no_data_found then
-- SELECT didn't return anything, but raised an exception
message('Wrong username');
message('Wrong username');
end;