//返回类型,0:密码更改成功,1:旧密码错误,2:密码更改不成功,请重试
 public int ChangePassword(int studentId, string oldPassword, string newPassword)
 {
     //IStudentDao studentDao = new StudentDao(sessionFactory);
     Student selectedStudent=studentDao.Get(studentId);
     if (selectedStudent != null)
     {
         if (oldPassword!=selectedStudent.studentPassword)
         {
             return 1;
         }
         else {
             selectedStudent.studentPassword = newPassword;
             ISystemUserDao systemUserDao = new SystemUserDao(sessionFactory);
             SystemUser selectedSystemUser = systemUserDao.Get(selectedStudent.studentID.ToString());
             selectedSystemUser.systemUserPassword = newPassword;
             try
             {
                 studentDao.Update(selectedStudent);
                 systemUserDao.Update(selectedSystemUser);
                 return 0;
             }
             catch (Exception e) {
                 return 2;
             }
         }
     }
     else {
         return 2;
     }
 }
        //登陆
        public Domain.SystemUser Login(string id, string password)
        {
            ISystemUserDao newUserDao = new SystemUserDao(sessionFactory);

             SystemUser newUser = newUserDao.Get(id);
             if (newUser != null){
                 if (password == newUser.systemUserPassword){
                     return newUser;
                 }
                 else{
                     return null;
                 }
             }
             else{
                 return null;
             }
        }