Question

运行代码时出现此异常我再次尝试但我不断得到它问题是学生无法进行测试，因为一个人这次给它同步类型的错误即将到来

...

Caused by: org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)

我的代码：

公共同步StudentAnswer saveAnswer（用户用户，String assignmentid，String answerid，String answer）抛出异常{

    if (user == null || user.getStudent() == null)
        throw new GeneralSecurityException("Permission Denied");

    Auditor auditor = new Auditor(user);

    AssignmentStatus status = getAssignmentStatus(user, assignmentid);
    StudentAnswer studentAnswer = getStudentAnswer(user, assignmentid, answerid);

    Object oldStatus = auditor.clone(status, new AssignmentStatus());
    //Object oldAnswer = auditor.clone(studentAnswer, new StudentAnswer());
    Object oldAnswer = auditor.clone((studentAnswer == null) ? new StudentAnswer() : studentAnswer, new StudentAnswer());
    Date now = new Date();

    if (status != null && status.isCompleted())
        return studentAnswer;

    if (studentAnswer == null) {

        Assignment assignment   = getAssignment(user, assignmentid);
        AnswerKey answerKey     = (AnswerKey) genericDao.get(AnswerKey.class, answerid);

        if (answerKey == null)
            throw new Exception("There was an error trying to save an answer.");

        if (status == null)
            status = startAssignment(user, assignment, now);

        if (status == null)
            throw new Exception("There was an error trying to start the assignment.");

        studentAnswer = new StudentAnswer();
        studentAnswer.setStudent(user.getStudent());
        studentAnswer.setCreateTime(now);
        studentAnswer.setAssignmentStatus( status );
        studentAnswer.setAssignment(assignment);
        studentAnswer.setAnswerKey( answerKey );
        studentAnswer.setQuestionNumber( answerKey.getNumber() );
        studentAnswer.setAnswerKeyCopy( answerKey.getAnswer() );

        //Adding a new answer changes your progress percentage, so we recalculate it
        updateProgress(status, now, answer);

    }
    //changing existing answer
    else {
        Long practiceId = studentAnswer.getAnswerKey().getPractice().getObjectid();

        PracticeStatus practiceStatus = null;
        for (PracticeStatus tmpPracticeStatus : (List<PracticeStatus>) status.getPracticeStatuses()) {
            if (tmpPracticeStatus.getCustomPractice().getPractice().getObjectid().longValue() == practiceId.longValue()) {
                practiceStatus = tmpPracticeStatus;
            }
        }

        //completed practice due to time out or submit?  Don't change the
        //answer.
        if (practiceStatus != null && practiceStatus.isCompleted()) {
            throw new Exception("Time is up for this practice, so answers may no longer be changed.");
            //return studentAnswer;
        }

    }

    if (answer!=null && answer.length() > 0)
        studentAnswer.setAnswer(answer.charAt(0));
    else
        studentAnswer.setAnswer(' ');

    studentAnswer.setUpdateTime(now);


    studentAnswer = (StudentAnswer) genericDao.save(studentAnswer);

    updateGrade(status);
    updateProgress(status, now, null);
    genericDao.save(status);

    auditor.audit("answer_save", status, oldStatus);
    auditor.audit("answer_save", studentAnswer, oldAnswer);
    genericDao.saveList(auditor.getList());

    return studentAnswer;
}

Answer 1

这可能意味着在您的事务提交之前，您尝试更新的行已经被其他一些线程更新过。检查多个线程是否同时处理相同的记录。

Answer 2

我认为你的问题是为什么你得到这个例外以及如何解决它。如果您的系统对并发更新的容忍度为零，那么在查询中使用悲观锁定，但您必须确保在短事务中获得锁定，否则会出现性能问题。或者更好的解决方案是使用乐观锁（使用版本字段）并检查版本是否等于最新版本，如果不可能向用户发送消息说数据已过期。

行被另一个事务更新或删除

2 个答案: