Error when execuuting Before Insert Trigger

Question

I have an Oracle, apex application with a MasterDetail Form. I need to do a BeforeInsert Trigger for the details part of the form. I need to populate the fields for the BEFOREINSERT_CHARGES with the data from another table (AHAR_PARTSLABOR) This is what I have so far yet it keeps giving me a message error:

ORA-04082: NEW or OLD references not allowed in table level triggers.

CREATE OR REPLACE Trigger BEFOREINSERT_CHARGES
BEFORE INSERT
On AHAR_REPAIRORDER_CHARGES

--DECLARAR VARIABLES
     --T_CHARGES_TYPE IN CHAR(11);
     --T_CHARGES_PRICE IN NUMBER;
     --T_CHARGES_DISCOUNT IN NUMBER; 

    --VALIDAR QUE EL CHAR_CODE INGRESADO POR EL USUARIO EXISTA

BEGIN

--SELECT PARA PASAR LOS VALORES DE PARTSLABOR A CHARGES 

    SELECT (PARTLABOR_TYPE, PARTLABOR_PRICE, PARTLABOR_DISCOUNT)
    INTO (:NEW.CHARGES_TYPE, :NEW.CHARGES_PRICE, :NEW.HARGES_DISCOUNT)

    FROM AHAR_PARTSLABOR
    WHERE :NEW.CHARGE_CODE = PARTLABOR_ID;

END;

Answer 1

In order to be able to change the :new values you have to use a "for each row" trigger:

CREATE OR REPLACE Trigger BEFOREINSERT_CHARGES
BEFORE INSERT
On AHAR_REPAIRORDER_CHARGES FOR EACH ROW