google app engineのJDOをさわっているけどdetach周りの挙動がよくわからん。

ClassNotDetachableExceptionが発生したりする。

The class "study.model.Oya" is not Detachable. This means that the MetaData for the class did not have the "detachable" attribute set to true.
org.datanucleus.exceptions.ClassNotDetachableException: The class "study.model.Oya" is not Detachable. This means that the MetaData for the class did not have the "detachable" attribute set to true.
  at org.datanucleus.ObjectManagerImpl.assertDetachable(ObjectManagerImpl.java:3847)
  at org.datanucleus.ObjectManagerImpl.detachObject(ObjectManagerImpl.java:1765)
  at org.datanucleus.store.fieldmanager.DetachFieldManager.processPersistable(DetachFieldManager.java:89)
  at org.datanucleus.store.fieldmanager.DetachFieldManager.internalFetchObjectField(DetachFieldManager.java:118)
  at org.datanucleus.store.fieldmanager.AbstractFetchFieldManager.fetchObjectField(AbstractFetchFieldManager.java:104)
  at org.datanucleus.state.JDOStateManagerImpl.detach(JDOStateManagerImpl.java:3469)
  at org.datanucleus.ObjectManagerImpl.performDetachOnClose(ObjectManagerImpl.java:3263)
  at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:767)
  at org.datanucleus.jdo.JDOPersistenceManager.close(JDOPersistenceManager.java:270)
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
public class Oya {

するか
jdoconfig.xmlに下記を記載すればOK? 上下は同じこと指してるの?

<property name="datanucleus.DetachOnClose" value="false"/>

それとも
Persistent.createManager().detachCopyAll()使えってこと??
 
このあたりの情報がWebでうまいこと見つけられない・・・。
どこにあるんだろう。書籍も探してみるか。JDO本を探せばいいのかな。