Кроме как в on-error перехватить ORA-00001 при коммите формы врятли получится, если блок не построен на транзакционных триггерах или процедурах. Пользуйтесь хелпом, в формсах он вполне полноценный.
DBMS_ERROR_CODE examples:
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/*
** Built-in: DBMS_ERROR_CODE,DBMS_ERROR_TEXT
** Example: Reword certain Form Builder error messages by
** evaluating the DBMS error code that caused them
** Trigger: On-Error
*/
DECLARE
errcode NUMBER := ERROR_CODE;
dbmserrcode NUMBER;
dbmserrtext VARCHAR2( 200 );
BEGIN
IF errcode = 40508 THEN
/*
** Form Builder had a problem INSERTing, so
** look at the Database error which
** caused the problem.
*/
dbmserrcode := DBMS_ERROR_CODE;
dbmserrtext := DBMS_ERROR_TEXT;
IF dbmserrcode = - 1438 THEN
/*
** ORA-01438 is "value too large for column"
*/
Message('Your number is too large. Try again.');
ELSIF dbmserrcode = - 1400 THEN
/*
** ORA-01400 is "Mandatory column is NULL"
*/
Message('You forgot to provide a value. Try again.');
ELSE
/*
** Printout a generic message with the database
** error string in it.
*/
Message('Insert failed because of '||dbmserrtext);
END IF;
END IF;
END;
