How to copy custom field creating child orders action

public class SOOrderEntry_Extension : PXGraphExtension<PX.Objects.SO.SOOrderEntry>
    {
        #region Event Handlers

        public SelectFrom<SOLine>.View SolineView;

        protected void _(Events.RowUpdated<SOLine> e)
        {
            SOLine row = e.Row;
            SOLine oldrow = e.OldRow;
            if (row !=null)
            {
                if (row.BlanketNbr == null)
                    return;
                SOLineExt solineext = row.GetExtension<SOLineExt>();
                SOLineExt oldsolineext = oldrow.GetExtension<SOLineExt>();
                if (oldsolineext.UsrUserDescription == null && solineext.UsrUserDescription == null)
                {   
                    if (row.BlanketNbr != null)
                    {
                        var SolineItems = SolineView.Select()
                            .Where(item => item.GetItem<SOLine>()
                            .OrderNbr == row.BlanketNbr).Where(item => item.GetItem<SOLine>()
                            .LineNbr == row.BlanketLineNbr);
                        foreach (SOLine line in SolineItems)
                        {
                            if (line.LineNbr == row.BlanketLineNbr)
                            {
                                solineext.UsrUserDescription = line.GetExtension<SOLineExt>().UsrUserDescription;
                            }
                        }
                    }
                }
            }

        }
        #endregion

    }