detached entity passed to persist: JPA inheritance

Question

I have a class Bus which inherits from Vehicle. It's a JPA Single table inheritance (the discriminator column is TYPE : "B" for bus). When I try to persist a Bus, i get this error. what can be the reason? thanks

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 

code causing the error :

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

the insertVehicle method uses entitymanager.persist

@Override
public Vehicle insertVehicle(Vehicle vehicle) {

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

Answer 1

According to the log, the Vehicle contains an association to a VehicleStatus entity or entities.

The 'detached entity passed to persist' error is given because the persist operation is cascaded to VehicleStatus too.

The easiest fix is to call merge instead of persist:

@Override
public Vehicle insertVehicle(Vehicle vehicle) {

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