How to carry out entry validation in SM30 with events

Question

Hi people,
I'm creating a Z table with Maintenance view in SM30...i've modified the view so all fields are required as Rich H explained in some other post. But now i need to validate user input for a particular field against a standard table, and force to reenter if data is not valid. I've been looking up the available events...event 05 triggers when the line is new, but not when modifying. I've tried a couple of other events but don't serve my purpose. What i want is to validate data upon user's entered all the required fields (whether the line was preeexistant or  not). If data is valid then go on, if not trigger a message and force correction prior continuing (disallowing saving).
Anyone knows how to do this?
Many thanks

Answer 1

I get what you suggest, but unfortunately i've already done that, it's not enough.
Here's the situation: The table has this fields:
KSCHL (PK-FK T685)
LIFNR (PK-FK LFA1)
EBELN (FK EKKO)
EBELP (FK EKPO)
Besides the implicit foreign key validations (i.e. the PO item exists in EKPO), i need to validate that it's not deleted (LOEKZ = 'L') and that the PO vendor is the one entered (i must not enter any PO which vendor isn't the one in that line). Hope I make myself clear.
This code works but in event 05 (new lines). I need to find out an event for the modified lines as well:
FORM f_validate_po.
  CHECK NOT ( ztmmiv001rps-lifnr IS INITIAL OR
              ztmmiv001rps-ebeln IS INITIAL OR
              ztmmiv001rps-ebelp IS INITIAL ).
  SELECT COUNT(*)
  FROM ekko
  WHERE ebeln = ztmmiv001rps-ebeln AND
        lifnr = ztmmiv001rps-lifnr AND
        exists ( SELECT *
                 FROM ekpo
                 WHERE ebeln = ztmmiv001rps-ebeln AND
                       ebelp = ztmmiv001rps-ebelp AND
                       loekz <> 'L' ).
  IF sy-dbcnt = 0.
    MESSAGE e000.
  ENDIF.
ENDFORM.