public IActionResult RentableBookItem(string barcode) { if (string.IsNullOrEmpty(barcode)) { return(Content("")); } var inventoryItem = _inventoryProvider.FindInventoryItemByBarcode <Book>(barcode); if (inventoryItem == null) { inventoryItem = _inventoryProvider.FindInventoryItemByExternalId <Book>(barcode); } //TODO: write proper error handling, with error message on client site if (inventoryItem == null) { return(Content("")); } //TODO: show error if book is allready rented by someone else return(PartialView("_RentInventoryItem", inventoryItem)); }