JPA：删除所有条目，然后在一个事务中重新创建单个条目

Question

我有一个问题，我想从一个表中删除所有条目，然后从头开始重新创建具有与已删除条目相同 ID 的单个条目。这应该在一个事务中，以便表永远不会为空。

提示：我使用 Spring Batch 并通过块侦听器 beforeChunk（在事务内部）删除 talbe，读取器/写入器随后运行以保存新版本的数据。

目前，如果我这样做，我会收到此错误：

Encountered an error executing step importXXXXX in job jobXXXX java.lang.IllegalArgumentException: Cannot merge an Entity that has been removed

堆栈跟踪：

at org.eclipse.persistence.internal.sessions.MergeManager.registerObjectForMergeCloneIntoWorkingCopy(MergeManager.java:1070) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.sessions.MergeManager.mergeChangesOfCloneIntoWorkingCopy(MergeManager.java:564) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.sessions.MergeManager.mergeChanges(MergeManager.java:313) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.mergeCloneWithReferences(UnitOfWorkImpl.java:3521) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.mergeCloneWithReferences(RepeatableWriteUnitOfWork.java:387) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.mergeCloneWithReferences(UnitOfWorkImpl.java:3481) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.mergeInternal(EntityManagerImpl.java:553) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.merge(EntityManagerImpl.java:530) ~[eclipselink-2.6.4.jar:2.6.4.v20160829-44060b6]
at org.springframework.batch.item.database.JpaItemWriter.doWrite(JpaItemWriter.java:104) ~[spring-batch-infrastructure-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.item.database.JpaItemWriter.write(JpaItemWriter.java:83) ~[spring-batch-infrastructure-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.item.SimpleChunkProcessor.writeItems(SimpleChunkProcessor.java:175) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.item.SimpleChunkProcessor.doWrite(SimpleChunkProcessor.java:151) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.item.SimpleChunkProcessor.write(SimpleChunkProcessor.java:274) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.item.SimpleChunkProcessor.process(SimpleChunkProcessor.java:199) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.item.ChunkOrientedTasklet.execute(ChunkOrientedTasklet.java:75) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:406) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:330) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133) ~[spring-tx-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at org.springframework.batch.core.step.tasklet.TaskletStep$2.doInChunkContext(TaskletStep.java:271) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.scope.context.StepContextRepeatCallback.doInIteration(StepContextRepeatCallback.java:81) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.repeat.support.RepeatTemplate.getNextResult(RepeatTemplate.java:374) ~[spring-batch-infrastructure-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.repeat.support.RepeatTemplate.executeInternal(RepeatTemplate.java:215) ~[spring-batch-infrastructure-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.repeat.support.RepeatTemplate.iterate(RepeatTemplate.java:144) ~[spring-batch-infrastructure-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.tasklet.TaskletStep.doExecute(TaskletStep.java:257) ~[spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:200) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:148) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:64) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:67) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:169) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:134) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:306) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:135) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]
at org.springframework.core.task.SyncTaskExecutor.execute(SyncTaskExecutor.java:50) [spring-core-4.3.7.RELEASE.jar:4.3.7.RELEASE]
at org.springframework.batch.core.launch.support.SimpleJobLauncher.run(SimpleJobLauncher.java:128) [spring-batch-core-3.0.7.RELEASE.jar:3.0.7.RELEASE]

您是否有保留该条目的想法，尽管它已在此事务中删除。

谢谢！

Answer 1

specification 在3.2.4.1 合并分离实体状态部分中有以下内容：

如果 X 是已移除的实体实例，则合并操作将抛出 IllegalArgumentException（否则事务提交将失败）。

它还在3.2.1 持久化实体实例部分中说：

如果 X 是一个被移除的实体，它就会变成托管的。

在3.2.3 同步到数据库小节中更进一步：

如果 X 是托管实体，则将其同步到数据库。

[...]

• 如果 X 是已删除的实体，则将从数据库中删除。没有相关的级联选项。

因此，您尝试使用 JPA 做的事情似乎是不可能的。一种解决方法可能是我的评论中建议的实体重用。