Supplementary Item Quantity Validation in PO confirm.

My requirement is throwing validation based on the Quantity of supplementary items when a purchase order is for confirmation. 

 [ExtensionOf(classStr(PurchFormLetter_PurchOrder))]

public final class  DAX_PurchFormLetter_Extension

{

   public boolean validate(Object _calledFrom)

   {

       boolean         retExt = next validate(_calledFrom);

       boolean         ret1 = true,ret2;

       PurchLine       purchLineExt,purchline;

       SuppItemTable   suppItemTable;

       str             id;

       id = this.purchTable().PurchId;

       if (retExt)

       {

          while select * from purchline

             where purchline.purchid == id

           {

               ret1 = true;

              while select * from suppItemTable

                   where suppItemTable.ItemRelation == purchline.ItemId

               {

                   if(suppItemTable)

                   {

                       select * from purchLineExt

                           where purchLineExt.ItemId == suppItemTable.SuppItemId

                           && purchLineExt.PurchId == purchline.PurchId;

 

                            if (!purchLineExt)

                            {

                               ret1 = false;

                            }

                     }

 

               }

           

               if(ret1 == false )

               {

                   ret1 =  checkFailed(strFmt("please select the supplimentory items for %1  ",purchline.ItemId));

                   return  ret1;

               }

               

               if(purchline.PurchQty != suppItemTable.SuppItemQty )          

                     {

               ret2 =  checkFailed(" Please enter the supplimentory quantity  and purchline quantity should be equal");

                   return ret2;

             }

            }

       }

RESULT:-