org.hibernate.internal.ExceptionMapperStandardImpl.mapManagedFlushFailure HHH000346：托管刷新期间出错

如何解决org.hibernate.internal.ExceptionMapperStandardImpl.mapManagedFlushFailure HHH000346：托管刷新期间出错

我有一个服务器错误：

    ListView.builder(
        reverse: true,itemBuilder: (context,int index) {
          /// separate Feed by dates
          Widget separator = SizedBox();
          if (index != 0 && messages[index].createdAt.day != messages[index - 1].createdAt.day) {
            separator = Container(
              height: 2,width: Get.width,color: Colors.black,);
          }
          return Column(
            children: [
              separator,MessageBubbleWidget(messages[index]),],);
        });

在浏览器中看起来像这样：

> ERROR [http-nio-8080-exec-5]
> org.hibernate.internal.ExceptionMapperStandardImpl.mapManagedFlushFailure
> HHH000346: Error during managed flush [Row was updated or deleted by
> another transaction (or unsaved-value mapping was incorrect) :
> [com.javaschool.ev.domain.Train#0]]

我想念乐观锁 (Baeldung)，不过对于版本化实体，默认情况下乐观锁是可用的。

如何以及在何处明确请求乐观锁？

我曾尝试在 TrainDAOImpl 中执行此操作，但 IDE 无法解析 OPTIMISTIC_INCREMENT。（代码如下）

HTTP Status 500 – Internal Server Error
Type Exception Report
Message Request processing Failed; nested exception is org.springframework.orm.hibernate5.HibernateOptimisticLockingFailureException: Object of class [com.javaschool.ev.domain.Train] with identifier [0]: optimistic locking Failed; nested exception is org.hibernate.staleobjectstateexception: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.javaschool.ev.domain.Train#0]
Description The server encountered an unexpected condition that prevented it from fulfilling the request.
Exception
org.springframework.web.util.nestedservletexception: Request processing Failed; nested exception is org.springframework.orm.hibernate5.HibernateOptimisticLockingFailureException: Object of class [com.javaschool.ev.domain.Train] with identifier [0]: optimistic locking Failed; nested exception is org.hibernate.staleobjectstateexception: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.javaschool.ev.domain.Train#0]

这是我的project in Github

在此先非常感谢您！

干杯， 卡特里热