[Java] JDO - Updating an Object

Question

Hi, i am experimenting with the Google App Engine, and the persist option JDO. I would like to know if it is possible to map a transient object to a persist object? Or something to update the persistent object with the use of an transient object?

I the coding examples i see the following piece of code to update objects:

public void updateEmployeeTitle(User user, String newTitle) {
PersistenceManager pm = PMF.get().getPersistenceManager();
try {
    Employee e = pm.getObjectById(Employee.class, user.getEmail());
    if (titleChangeIsAuthorized(e, newTitle) {
        e.setTitle(newTitle);
    } else {
        throw new UnauthorizedTitleChangeException(e, newTitle);
    }
} finally {
    pm.close();
}
}

But this is not what i want, does anybody know if i can update the whole object like JPA does: object.update();

So i would like something like this:

public User update(User u) {
 PersistenceManager pm = PMF.get().getPersistenceManager();
 User usr;
 try {
  usr = pm.getObjectById(User.class, u.getId());
  // copy transient object u to persist object usr.
                    // on update of usr all changes in object u are persistent.

 } finally {
  pm.close();
 }

 return u;
}

Answer 1

A "transient" object has no "identity" so there is no way to locate it in a datastore. Think carefully if you want to use transient objects, or whether it would be better to just use detached objects. JPA uses the equivalent of a "detached" object. JDO can do that too and then you just call pm.makePersistent(detachedObj);

--Andy (DataNucleus)