Show a insert trigger error message on a compiled form

Question

Good Morning
Is there any way to get a oracle complied form to display a message
from a trigger insert event.
My problem is that we have proprietry oracle froms application (with compiled
forms and no source code. I need to raise some sort of warning message
from the form when certain condition occurs.
I have tried using some code like below in the trigger
but the dbms_output.put_line does not output anything
nor the EXCEPTION
DECLARE MY_ERROR exception;
begin
DBMS_OUTPUT.ENABLE;
dbms_output.put_line('outputting this message');
raise MY_ERROR;
EXCEPTION
WHEN others THEN Raise;
END;
thanks
David Hills

Answer 1

You don't need to get at the source code of the form. The example you gave will stop the execution of any process and you said it should happen for an insert event. So a Raise_Application_Error in a database trigger would be sufficient.
Hopefully the vendor has put code in their on-error triggers which will cut the message out of a user-defined exception and display it as an alert (this is so much a better method than returning numbers to indicate success or type of failure). If not then the message will be rather ugly but it will at least get the job done.
James.