How to use JDO(DataNucleus) to Update & Delete data?

Question

I've set up a small project using apache.JDO /w DataNucleus. I can save data w/o any problems, but I got stuck when trying to update or delete them.

The scenario is the following:

1. I create an object & persist it, it gets and id

     @PrimaryKey  
     @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)  
     private Long id;  

2. I close the PersistenceManager
3. In the app I modify my object (Transient)
4. I try to persist again (the id field is the same), but instead of update it results in the creation of a new object

In Google App Engine the same scenario gave me an update (the expected results - see below).

I will also give you a small code sample to exemplify my problem:

        PersistenceManager pm = PMF.getPM();
        Option dao = new Option(String.class, "field", "A");
        pm.makePersistent(dao);
        pm.close();

        System.out.println("1");
        for (Object o : Model.findAll(Option.class))
            System.out.println(((Option) o).getValue());

        dao.setValue("B");

        pm = PMF.getPM();
        pm.makePersistent(dao);
        pm.close();

        System.out.println("2");
        for (Object o : Model.findAll(Option.class))
            System.out.println(((Option) o).getValue());

        pm = PMF.getPM();
        pm.makePersistent(dao);
        pm.deletePersistent(dao);
        pm.close();

        System.out.println("3");
        for (Object o : Model.findAll(Option.class))
            System.out.println(((Option) o).getValue());

I would expect the output to be:

1
A
2
B
3

But instead it gives me:

1
A
2
A
B
3
A
B

Any suggestions on what am I doing wrong? (btw I use non-transactional RW, with RetainValues enabled)

Answer 1

I've solved my problem (@point 2)

pm = PMF.getPM();
dao = pm.getObjectById(DO.class, 1L);
dao.setValue("B");
pm.makePersistent(dao);
pm.close();

But this solutions is somewhat costly if I have 70-100 fields, because I have to set each separately.

I haven't done it manually, but with reflection - but then what's the advantage of DataNucleus over Hibernate? - which (as far as I know) also uses runtime introspection.

Please correct me if I'm wrong - I'm still a newbie in this area... yet :)

Answer 2

You don't need to call makePersistent agian.

long id = objectId; //Id of the object you want to update.

pm = PMF.getPM();

DO dao = pm.getObjectById(DO.class, id);
dao.setValue("B");

pm.close();

To delete do this;

long id = objectId; //Id of the object you want to delete.
pm = PMF.getPM();

DO dao = pm.getObjectById(DO.class, id);
pm.deletePersistent(dao);

pm.close();

You are not using transaction to commit. You can look at DataNucleus docs