问题： 控制台save the transient instance before flushing，object references an unsaved transient instance

org.springframework.dao.InvalidDataAccessApiUsageException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing :Data ->Data; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : 
at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:371)
at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:257)
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:538)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:743)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:711)
at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:633)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:386)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:118)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor

.
CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:178)atorg.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)atorg.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95)atorg.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)atorg.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212)atcom.sun.proxy.Proxy172.save(Unknown Source)

at serial.ReadThread.run(ReadThread.java:57)
Caused by: java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : 
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:151)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:181)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:188)
at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1366)
at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:453)
at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:3212)
at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2380)
at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:448)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:183)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access

300(JdbcResourceLocalTransactionCoordinatorImpl.java:40)atorg.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImplTransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:281)
at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:101)
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:534)
... 17 more
Caused by: org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : com.test.Data
at org.hibernate.engine.spi.CascadingActions$8.noCascade(CascadingActions.java:379)
at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:169)
at org.hibernate.event.internal.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:159)
at org.hibernate.event.internal.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:149)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:82)
at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:39)
at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:99)
at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1362)
... 26 more

解决方案
这个异常堆栈信息显示了在Spring Data JPA与Hibernate配合使用时遇到的一个常见问题，即尝试在持久化实体时，它关联的属性是一个未被保存的瞬态实例。根据Hibernate的工作机制，在flush操作期间，如果发现一个持久化实体引用了未经持久化的关联对象，就会抛出TransientPropertyValueException异常。

解决这个问题的方法如下：

1、在调用.save之前，确保先保存或更新其关联的实例：

// 假设有个实体
Test1 test= ... // 创建或获取test1实例
testService.save(test); // 先保存DeviceData
Test2 test2=
test2.setLastData(test.testId);
test2Service.save(cntrnum); // 现在可以安全地保存Cntrnum

2、如果实体之间存在级联关系（Cascade），并且你应该在保存Cntrnumber时自动保存DeviceData，请检查你的实体类中对应的@ManyToOne或@OneToOne注解是否配置了正确的cascade策略，如CascadeType.PERSIST或CascadeType.ALL。

@Entity
public class Test1{
    @ManyToOne(cascade = CascadeType.ALL)
    private Test2 test2 ;
    // ...
}