private bool FilterOrders(Order entity)
 {
     return (entity.CustomerID == this.CustomerID);
 }
 private void AttachOrders(Order entity)
 {
     entity.Customer = this;
 }
 private void DetachOrders(Order entity)
 {
     entity.Customer = null;
 }
 private bool FilterOrder(Order entity)
 {
     return (entity.OrderID == this.OrderID);
 }