一对多关联关系的级联操作--cascade_一对多可以级联吗-优快云博客

本文探讨了在使用Hibernate进行对象持久化时，级联操作与对象实例保存之间的关系，解释了如何在Department映射文件中配置级联以避免TransientObjectException错误，并详细分析了错误产生的原因及解决方案。

如果employee的实例没有save，但是在映射文件Department.hbm.xml中添加cascade（级联操作），也可以保存。

<list name="emp2" cascade="save-update">
			<key column="depart_id" />
			<list-index column="list_index" />
			<one-to-many class="Employee" />
		</list>

否则会报错，如下：

Hibernate: insert into Department (name) values (?)
Hibernate: update Employee set depart_id=?, list_index=? where id=?
Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.messi.hibernate.domain.Employee
   at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:219)
   at org.hibernate.type.EntityType.getIdentifier(EntityType.java:397)
   at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:78)
   at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:755)
   at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1143)
   at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:26)
   at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:250)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:234)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:145)
   at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
   at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
   at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
   at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
   at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
   at com.messi.hibernate.test.Many2one.add(Many2one.java:49)
   at com.messi.hibernate.test.Many2one.main(Many2one.java:14)