public IHttpActionResult PostInventoryItem(InventoryItem inventoryItem)
        {
            if (!ModelState.IsValid|| inventoryItem.ProductId ==0)
            {
                return BadRequest(ModelState);
            }

            _inventoryService.Insert(inventoryItem);
            _inventoryService.SaveChanges();

            return CreatedAtRoute("DefaultApi", new { id = inventoryItem.Id }, inventoryItem);
        }
        public IHttpActionResult PutInventoryItem(int id, InventoryItem inventoryItem)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

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

            _inventoryService.Update(inventoryItem);

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

            return StatusCode(HttpStatusCode.NoContent);
        }