public void Update(Order order)
 {
     using (var db = new OrderDB())
     {
         db.Order.Attach(order);
         db.Entry(order).State = EntityState.Modified;
         order.Items.ForEach(item => db.Entry(item).State = EntityState.Modified);
         db.SaveChanges();
     }
 }
 public void Add(Order order)
 {
     using (var db = new OrderDB())
     {
         db.Entry(order).State = EntityState.Added;
         db.SaveChanges();
     }
 }