how to avoid getting duplicated sales orders into my custom screen?

Hi,

I have customized a new screen. To my screen I’m getting data from soorder DAC and soline DAC. This time, I need to get sales orders without duplicating from the view to my custom screen. When new row is inserted into my line level, I need to update TotalDiscount field of header level with soorder.curydisctot value which is taken from the soorder screen header level. To accomplish avoid duplicating when adding same sales order number , I tried the below code in the row inserted event but it didn’t work.

protected void APProformaItemList_RowInserted(PXCache cache, PXRowInsertedEventArgs e) 
        {
            var row = (APProformaItemList)e.Row;
            APProforma item = APProformas.Current;

            //add so discount into form
            var distinctSOLines = this.APProformaItems.Select().FirstTableItems.ToList().Select(x => x.Ponbr).Distinct();

            foreach(var itemlist in distinctSOLines)
            {

                SOOrder order= SelectFrom<SOOrder>.Where<SOOrder.orderNbr.IsEqual<SOOrder.orderNbr>>.View.Select(this, itemlist);

                item.TotalDiscount = item.TotalDiscount+order.CuryDiscTot;
            }
        }

APProformaItemList - line level dac

APProforma - header leveldac

ApproformaItems - line level view

ponbr= foreign reference with soline dac

Have I done something wrong in this code or is there any other work around to accomplish this? can someone help me with this?

Thank you in advance.