how to optionally sum multiple has many

    field on bulkOrder {
  (sum(cast(draftOrders.subtotalPrice, type: "Number")) - 
    (customer.bulkOrderPercentDiscount ? 
      (sum(cast(draftOrders.subtotalPrice, type: "Number")) * (customer.bulkOrderPercentDiscount / 100)) 
      : 0)) + 
    sum(cast(draftOrders.totalTax, type: "Number")) +
     sum(cast(draftOrders.shippingLine.price, type: "Number"))
}