相关疑难解决方法(0)

我有一个引用实体Bar的实体Foo:

@Entity
public class Foo {

    @OneToOne(cascade = {PERSIST, MERGE, REFRESH}, fetch = EAGER)
    public Bar getBar() {
        return bar;
    }
}

当我坚持使用新的Foo时,它可以获得对新Bar或现有Bar的引用.当它获得一个恰好分离的现有Bar时,我的JPA提供程序(Hibernate)抛出以下异常:

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.example.Bar
 at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:102)
 at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:636)
 at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:628)
 at org.hibernate.engine.EJB3CascadingAction$1.cascade(EJB3CascadingAction.java:28)
 at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:291)
 at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:239)
 at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:192)
 at org.hibernate.engine.Cascade.cascade(Cascade.java:153)
 at org.hibernate.event.def.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:454)
 at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:288)
 at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
 at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
 at org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:49)
 at org.hibernate.event.def.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:154)
 at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:110)
 at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:61)
 at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:645)
 at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:619)
 at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:623)
 at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:220)
 ... 112 more

当我确保管理(附加)Bar的引用或者在关系中省略级联PERSIST时,一切正常.

然而,这两种方案都不是100%令人满意.如果我删除级联持续存在,我显然不能再坚持引用新的Bar了.在持久化之前引用Bar管理需要这样的代码:

if (foo.getBar().getID() != …