public IHttpActionResult PostOrderItemByTableId(int tableid, OrderItem item)
        {
            var order = db.Orders.Single(o => o.TableId == tableid);
            var _item = new OrderItem
            {
                OrderId = order.Id,
                ProductId = item.ProductId,
                Quantity = item.Quantity
            };

            return PostOrderItem(_item);
        }
        public IHttpActionResult PostOrderItem(OrderItem orderItem)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            db.OrderItems.Add(orderItem);
            db.SaveChanges();

            return CreatedAtRoute("DefaultApi", new { id = orderItem.Id }, orderItem);
        }
        public IHttpActionResult PutOrderItem(int id, OrderItem orderItem)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != orderItem.Id)
            {
                return BadRequest();
            }

            db.Entry(orderItem).State = EntityState.Modified;

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!OrderItemExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return StatusCode(HttpStatusCode.NoContent);
        }