public string Create(Attendance attendance)
        {
            try
            {
                dbContext.Attendances.Add(attendance);
                dbContext.SaveChanges();

                return Constants.AJAX_CREATE_SUCCESS_RETURN;

            }
            catch (Exception e1)
            {
                return "<p class='alert alert-danger'>出错了: " + e1.Message + "</p>";
            }
        }
        public string Edit(Attendance attendance)
        {
            try
            {
                dbContext.Entry(attendance).State = System.Data.Entity.EntityState.Modified;
                dbContext.SaveChanges();

                return Constants.AJAX_EDIT_SUCCESS_RETURN;
            }
            catch (Exception e1)
            {
                return "<p class='alert alert-danger'>出错了: " + e1.Message + "</p>";
            }
        }