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From cbeams <cbe...@gmail.com>
Subject Re: Query by interface
Date Sat, 01 Sep 2007 17:32:38 GMT

Here's another, perhaps even simpler cut at it:

@PersistenceCapable
public interface Person {}

@PersistenceCapable
@Implements(Person.class)
public class MyPerson implements Person {}

public class Main {

     @SuppressWarnings("unchecked")
     public static void main(String... args) {
         PersistenceManagerFactory pmf =  
JDOHelper.getPersistenceManagerFactory("jpox.properties");
         PersistenceManager pm = pmf.getPersistenceManager();
         Person inst = new MyPerson();

         System.out.println(inst);

         pm.currentTransaction().begin();
         pm.makePersistent(inst);
         pm.currentTransaction().commit();

         System.out.println(pm.newQuery(pm.getExtent(Person.class,  
true)).execute());
     }

}


When running the above, JPOX auto-creates the following schema:

CREATE
     TABLE myperson
     (
         myperson_id bigint(20) NOT NULL,
         PRIMARY KEY USING BTREE (myperson_id)
     )

CREATE
     TABLE personimpl
     (
         personimpl_id bigint(20) NOT NULL,
         PRIMARY KEY USING BTREE (personimpl_id)
     )


The output of the main() method is as follows:

org.jpox.test.MyPerson@7c28c
[]


After running, the MYPERSON table has 1 row (as expected), the  
PERSONIMPL table has 0 rows.

The query in the main method is only pulling back rows from the  
PERSONIMPL table, thus the empty list.

It seems strange to me that the implementation is creating its own  
implementation (PersonImpl) when I've clearly expressed that I want  
to provide my own (MyPerson).

Thanks,

- Chris

P.S.: the results are the same whether I use an extent as above, or  
just directly query on the interface.


On Sep 1, 2007, at 8:53 AM, Erik Bengtson wrote:

> Chris,
>
> I think you have to use the Implements annotation. Something like:
>
> 	@PersistenceCapable(table="person")
> @Implements(Person.class)
> 	public class MyPerson implements Person {}
>
>
>
> -----Message d'origine-----
> De : cbeams [mailto:cbeams@gmail.com]
> Envoyé : samedi 1 septembre 2007 9:14
> À : jdo-user@db.apache.org
> Objet : Query by interface
>
>
> 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) {
> 			PersistenceManagerFactory pmf =
> JDOHelper.getPersistenceManagerFactory("pmf.properties");
> 			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;
> 		}	
> 	}
>
> 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.
>
> Thanks,
>
> - Chris
>
> Chris Beams
>
>
>
>
>
>
>
>
>


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