public IActionResult Deposit(DepositWithdrawViewModel model) { var customers = _bankRepository.GetListOfCustomers(); var account = customers.SelectMany(i => i.Accounts.Where(x => x.Accountnumber.Equals(model.Account.Accountnumber))).SingleOrDefault(); if (account == null) { ModelState.AddModelError("", "The account number doesn't exist."); model.Account = null; return(View("DepositWithdraw", model)); } else { _bankRepository.DepositAccount(model.Sum, account); model.Account.Balance = account.Balance; return(View("DepositWithdraw", model)); } }