I really recommend you read the documentation:
http://code.google.com/appengine/docs/java/datastore/overview.html
You are trying to do things the datastore does not allow. It's so
different that a relational datastore, I think you'll find you're
constantly roadblocked if you don't become familiar with it.
On Aug 26, 5:42 am, midomarocain <elattar...@gmail.com> wrote:
> i use three class User , Type ,and Article :
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class User {
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private Key id;
>
> @Persistent
> private String login;
>
> @Persistent
> private Type type;
>
> .......
>
> }
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class Type {
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private Key key;
>
> .......
>
> }
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class Article {
>
> @PrimaryKey
> �...@persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private Long id;
>
> �...@persistent
> private User user;
>
> .....
>
> }
>
> --------------------------------
> I use this method to save the article :
>
> public static Article save(Article article, Long userId) {
> Article result = null;
> PersistenceManager pm = PMF.get().getPersistenceManager();
> try {
> // Getting the user by id
> Query query = pm.newQuery(User.class, "id ==
> idParam");
> query.declareParameters("Long idParam");
> List<User> users = (List<User>) query.execute(userId);
> User user = null;
> if (!users.isEmpty()) {
> user = users.get(0);
> }
>
> article.setUser(user);
>
> result = pm.makePersistent(article);
> } finally {
> pm.close();
> }
> return result;
> }
>
> the exception :
>
> javax.jdo.JDOFatalUserException: Detected attempt to establish Article
> (16) as the parent of User(14) but the entity identified by User(14)
> has already been persisted without a parent. A parent cannot be
> established or changed once an object has been persisted.
> at
> org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException
> (NucleusJDOHelper.java:354)
> at org.datanucleus.jdo.JDOPersistenceManager.jdoMakePersistent
> (JDOPersistenceManager.java:674)
> at org.datanucleus.jdo.JDOPersistenceManager.makePersistent
> (JDOPersistenceManager.java:694)
> ......
>
> thanks in advance
>
> On 25 août, 17:14, objectuser <kevin.k.le...@gmail.com> wrote:
>
> > Can you tell us what the error is? And maybe some snippits of code
> > showing the relevant parts of your model and how it's mapped?
>
> > On Aug 25, 8:08 am, midomarocain <elattar...@gmail.com> wrote:
>
> > > I have a relation between a User and Article
>
> > > (1) User can have one or many article
>
> > > (2) an article is owned by only one user
>
> > > i'am intersted only by the relation (2)
>
> > > the User is persisted
>
> > > I create a new Article and i want relie it with an existant User
>
> > > But i have a probleme when trying to persist the article object
>
> > > my code is like
>
> > > article.setUser(user);
>
> > > pm.makePersistent(article);
>
> > > can any one help me please
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