public IActionResult AddProductPost(TransactionAddProductViewModel model) { if (_transactionManager.ActiveTransaction == null) { return(RedirectToAction("Index", "Transaction")); } Product product = _dataContext.Products.FirstOrDefault(q => q.Id == model.SelectedProductId); if (product == null) { ModelState.AddModelError(nameof(model.SelectedProductId), "Onbekend product"); return(View("AddProduct", new TransactionAddProductViewModel() { Products = _dataContext.Products })); } if (model.IsForSell) { _transactionManager.AddProductForSellToTransaction(product, model.NumberOfProducts, model.Points); } else { _transactionManager.AddProductToBuyToTransaction(product, model.NumberOfProducts, model.Points); } return(RedirectToAction("List")); }