数据不更新，仅在 EmployeeID 不等于 0 时添加记录

问：

public class EmployeeController : Controller
{
    public ActionResult EmployeeEarnings(int? employeeId)  //GET
    {
        if (employeeId.HasValue)
        {
            using (var dbContext = new EmployeeDbContext())
            {
                var employee = dbContext.EmployeeApplications.Find(employeeId);

                if (employee != null)
                {
                    return View(employee);
                }
            }
        }

        return View(new EmployeeApplication());
    }

    [HttpPost]
    public ActionResult EmployeeEarnings(List<EmployeeApplication> employees)
    {
        try
        {
            if (employees != null && employees.Count > 0)
            {
                using (var dbContext = new EmployeeDbContext())
                {
                    foreach (var employee in employees)
                    {
                        if (!ModelState.IsValid)
                        {
                            var errors = ModelState.Values.SelectMany(v => v.Errors)
                                .Select(e => e.ErrorMessage).ToList();

                            ModelState.Clear();

                            return Json(new { success = false, message = "Validation errors", errors = errors });
                        }

                        if (employee.Id != 0)
                        {
                            var existingEmployee = dbContext.EmployeeApplications.Find(employee.Id);

                            if (existingEmployee != null)
                            {
                                existingEmployee.EmpCode = employee.EmpCode;
                                existingEmployee.EmpName = employee.EmpName;
                                existingEmployee.January = employee.January;
                                existingEmployee.February = employee.February;
                                existingEmployee.March = employee.March;
                                existingEmployee.April = employee.April;
                                existingEmployee.May = employee.May;
                                existingEmployee.June = employee.June;
                            }
                            else
                            {
                                return Json(new { success = false, message = "Employee not found" });
                            }
                        }
                        else
                        {
                            dbContext.EmployeeApplications.Add(employee);
                        }
                    }

                    dbContext.SaveChanges();

                   return Json(new { success = true, message = "Data saved" });
                }
            }
            else
            {
                return Json(new { success = false, message = "No data" });
            }
        }
        catch (Exception ex)
        {
            return Json(new { success = false, message = "Error occurred: " + ex.Message });
        }
    }
}

这是jQuery：

$('#listTable').on('click', '.edit-button', function () {
    var employeeApplicationId = $(this).data('id');
    window.location.href = '/Employee/EmployeeEarnings?employeeId=' + employeeApplicationId;
});

我在代码中遇到了一个问题，即当 不等于 0 时，正在添加数据而不是更新数据。我已经彻底检查了我的代码，但找不到问题。EmployeeID

任何人都可以提供一些关于可能导致此行为的原因以及如何解决的指导或建议？提前致谢！