public ActionResult Save(ExpenseViewModel expense)
        {
            var expenseModel = expense.To <Expense>();

            if (ModelState.IsValid)
            {
                if (expenseModel.Id != default(Guid))
                {
                    _expenseApp.Update(expenseModel);
                }
                else
                {
                    _expenseApp.Add(expenseModel);
                }
            }

            return(Json(expenseModel, JsonRequestBehavior.AllowGet));
        }