System should not allow to delete PO line Item after GR/IR

Standard SAP will not allowed the PO to be deleted once it was GR done. The controlled is on the attributes of message to set as "E"
Message no. 06115
But if invoiced takes place, the is the point that PO can be deleted.
You have to do have a Enhancement using MM06E005, insert you logic here to check PO history tables like EKBE, then check if invoice " Q" (BEWTP) exist, the PO cannot be deleted once the user delete the PO line and SAVE it. Ask you developer to help you on the following coding.
Use MM06E005 and EXIT_SAPMM06E_012
IF SY-TCODE = 'ME22N'.
IF sy-ucomm = 'MESAVE' OR SY-UCOMM = 'YES'..
LOOP AT TEKPO.
IF TEKPO-LOEKZ = 'L'.
SELECT SINGLE BELNR FROM EKBE INTO BELNR1 WHERE EBELN = TEKPO-EBELN AND EBELP = TEKPO-EBELP AND BEWTP = 'E'.
IF SY-SUBRC = 0.
SELECT SINGLE BELNR FROM EKBE INTO BELNR2 WHERE EBELN = TEKPO-EBELN AND EBELP = TEKPO-EBELP AND BEWTP = 'Q'.
IF SY-SUBRC = 0.