Re: Query by interface

[Craig L Russell]

Hi Chris,






But for now, what if you don't map Person to the database?

Craig

On Sep 1, 2007, at 12:14 AM, cbeams wrote:

I guess you mapped both Person and MyPerson to the same tables in the database (and didn't add a discriminator column to distinguish Person from MyPerson). So the implementation thinks you want a generated Person to be constructed from the database rows. The discussion of persistent interfaces has not been translated into spec-language, and this is one of several use cases that need to be discussed.

As a user, here's what I would expect to work:


        @PersistenceCapable(table="person")
        public interface Person {}

        @PersistenceCapable(table="person")
        public class MyPerson implements Person {}


        public class Main {
                public static void main(String... args) {

                        PersistenceManager pm = pmf.getPersistenceManager();
                        
                        pm.currentTransaction().begin();
                        pm.makePersistent(new MyPerson());  // persist the 
concrete type
                        pm.currentTransaction().commit();

                        Query query = pm.newQuery(Person.class);  // query by 
the interface
                        query.setUnique(true);
                        Person person = (Person)query.execute();

                        assert person instanceof MyPerson == true;
                }       
        }





Thanks,

- Chris

Chris Beams

PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory("pmf.properties"); This does not work, however (at least with JPOX). My instanceof assertion at bottom fails, because person is actually a type generated by the implementation (PersonImpl in the case of JPOX). While I understand that this class generation approach may have some uses, I'm actually dealing with I believe is a much simpler use case that doesn't seem to be supported: I simply want to be able to persist an instance of a concrete type and subsequently query for that object by it's interface. Am I missing something? Note that I'm not looking for any JPOX- specific tips here; just some guidance on usage per the spec.

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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