Creating Trigger to auto increment PK value with Oracle

-- Start of DDL Script for Trigger HR.TRG_TEST
-- Generated 17-Dec-2009 14:39:33 from HR@ORCL
CREATE OR REPLACE TRIGGER hr.trg_test
BEFORE
INSERT
ON hr.dept
REFERENCING NEW AS n OLD AS o
FOR EACH ROW
BEGIN
SELECT dept_seq.nextval into :n.id from dual;
END;
/


-- End of DDL Script for Trigger HR.TRG_TEST