Master Table Summation of Detail Column

Master Table: "Stock"
Detail Table:  "UnitStockXrefUVO"

In my Master Table "Stock"we simply add the Transient Attribute "TotalSubQty";
as seen here below in the Attribute Detail Properites we have added the Transient Attribute TotalSubQty in Table "Stock"  and will use groovy to sum the column "SubQty" in Detail Table  "UnitStockXrefUVO"