java - 分离的实体传递到持久化 : JPA inheritance

Question

我有一个继承自 Vehicle 的 Bus 类。它是 JPA 单表继承(鉴别器列是 TYPE :“B”表示总线)。当我尝试保留总线时，出现此错误。可能是什么原因？谢谢

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: org.enseirb.it307.tp.entities.VehicleStatus
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:139)
    at org.hibernate.internal.SessionImpl.firePersistOnFlush(SessionImpl.java:838)
    at org.hibernate.internal.SessionImpl.persistOnFlush(SessionImpl.java:831)
    at org.hibernate.engine.spi.CascadingActions$8.cascade(CascadingActions.java:357)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:350)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:293)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:161)
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:379)
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:319)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:296)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:161)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:118)
    at 

导致错误的代码:

//Bus
Bus bus1 = BusTools.getSampleBus1();
createdToulouseOrg.addVehicle(bus1);
logger.info("insert Bus " + bus1);
Vehicle createdBus1 = vehicleDao.insertVehicle(bus1);

insertVehicle方法使用entitymanager.persist

@Override
public Vehicle insertVehicle(Vehicle vehicle) {

    entityManager.getTransaction().begin();
    entityManager.persist(vehicle);
    entityManager.getTransaction().commit();
    return vehicle;
}

Answer 1

根据日志，车辆包含与一个或多个 VehicleStatus 实体的关联。

出现“分离实体已传递到持久化”错误，因为持久化操作也级联到 VehicleStatus。

最简单的修复方法是调用 merge 而不是 persist:

@Override
public Vehicle insertVehicle(Vehicle vehicle) {

    entityManager.getTransaction().begin();
    vehicle = entityManager.merge(vehicle);
    entityManager.getTransaction().commit();
    return vehicle;
}