我有一个@Entity，默认情况下是Set的null。最初创建实体或在@Transactional方法中提取实体时对其进行更新时，一切正常。但是：当我尝试合并一个分离的实体时，我得到一个HibernateException，即使我根本没有碰到子级Set：@Entitypublic class MyEntity { @OneToMany(mappedBy = "myEntity", cascade = CascadeType.ALL, orphanRemoval = true) @OnDelete(action = OnDeleteAction.CASCADE) private Set<ChildEntity> child = null; //by default public Set<ChildEntity> getChild() { if (child == null) { child = new LinkedHashSet<>(); } return child; }}我可以保存实体而不必初始化子列表：@Transactionalpublic MyEntity create() { MyEntity entity = new MyEntity(); //set some params (but not the child object) dao.save(entity); return entity; //OK though child=null}但是以下合并失败：MyEntity entity = service.create(); //see aboversp = runLongTask();updateSomeParams(entity, rsp); //not touching childdao.merge(entity); //throws HibernateException结果：Caused by: org.hibernate.HibernateException: A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance: MyEntity.child at org.hibernate.engine.internal.Collections.processDereferencedCollection(Collections.java:114) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.engine.internal.Collections.processUnreachableCollection(Collections.java:67) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.event.internal.AbstractFlushingEventListener.flushCollections(AbstractFlushingEventListener.java:258) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:103) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:55) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1258) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:425) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:177) ~[hibernate-core-4.3.11.Final.jar:4.3.11.Final] at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:77) ~[hibernate-entitymanager-4.3.11.Final.jar:4.3.11.Final] at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:517) ~[spring-orm-4.2.6.RELEASE.jar:4.2.6.RELEASE] ... 33 more为什么不能将实体与null列表合并？如何防止该异常？ 最佳答案 由于您创建了一个新的子项（child = new LinkedHashSet （）;），每次子项为null时，您可以在create方法中尝试以下操作吗？@Transactionalpublic MyEntity create() { MyEntity entity = new MyEntity(); //set some params (but not the child object) entity.getChild().clear(); //Remove all of the elements from this set dao.save(entity); return entity; //OK though child=null}基本上，如果您不想进行设置，请从集合中删除所有元素
