2011/1/27 Jan Willies <j...@willies.info>
> Hi,
>
> I can't have my child-object have an order. The following code fails
> with:
>
> javax.jdo.JDOFatalUserException: Detected attempt to establish
> Topic(2) as the parent of SubTopic(9) but the entity identified by
> SubTopic(9) has already been persisted without a parent. A parent
> cannot be established or changed once an object has been persisted.
>
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION,
> detachable = "true")
> public class Topic {
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private Key key;
>
> @Order(extensions = @Extension(vendorName="datanucleus", key="list-
> ordering", value="position asc"))
> @Persistent(defaultFetchGroup = "true", mappedBy = "topic")
> @Element(dependent = "true")
> private List<SubTopic> subTopics = new ArrayList<SubTopic>();
>
> If I leave out the @Order everything works as expected. I do need the
> ordering however. Is there some other way to achive the same?
>
Ok, I solved it. What I did wrong (?) was that I added the children to the
parent outside a PersistenceManager, ie:
Topic topic = topicDao.findById(topicId);
SubTopic subTopic = new SubTopic();
topic.getSubTopics().add(subTopic);
topicDao.saveOrUpdate(topic);
Now I'm doing this:
Topic topic = pm.getObjectById(Topic.class, topicId);
topic.getSubTopics().add(subTopic);
pm.makePersistent(topic);
While I was at it, I added transactions. My DAO now looks like this:
@Override
public void addSubTopic(Long topicId, SubTopic subTopic) {
PersistenceManager pm = PMF.get().getPersistenceManager();
Transaction tx = pm.currentTransaction();
tx.begin();
try {
Topic topic = pm.getObjectById(Topic.class, topicId);
topic.getSubTopics().add(subTopic);
pm.makePersistent(topic);
tx.commit();
} finally {
try {
if (tx.isActive())
tx.rollback();
} finally {
pm.close();
}
}
}
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