Forms :: Updating Value Of Table From Textbox Which Is On Form

i m doin simple application, in which all data is retrieving from table in to form(all the

field are textbox and button on form) ename,dept,salary,dept_id etc.

i took one textbox field on form which is non table field

(no db field bt linked to another table..via LOV m retrieving value into this textbox which suppose dept_id ) and now after selecting one record from list box into textbox which is non table field.... after immdiately selecting i want to update one field into db field which all other form field contains...

so how to do this??which trigger i hav to use for this?

if :dept_id is not null then
begin
update dept
set loc =:emp.loc
where dept_id = :emp.dept_id;
forms_ddl('commit');
exception
when others then
null;
end;
end if;

it giving error.......if m using commit in this...i hav used post query trigger ...is dere

any other trigger hav to use