Problems using EntityManager.find for JOINED subclasses

frobb01 · **Joined:** Wed Jul 26, 2006 7:17 am **Posts:** 7

Hello,

I have a strange problem to retrieve an Entity by ID from the EntityManager using its find() method:

Code:

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class Owner {
    Long id;
    @Id
    @GeneratedValue
    public Long getId() {
        return id;
    }
    ...
}

@Entity
public class DmsUser extends Owner {
     ...
}

There is one DmsUser persisted with id 3, all tables are generated automatically, no caches enabled, MySql, Hibernate 3.2.0.cr3

If i use

Code:

1.: DmsUser user = EntityManager.find(DmsUser.class, new Long(3))

returns NULL !
but

Code:

2.: DmsUser user = (DmsUser) EntityManager.find(Owner.class, new Long(3))

works.

The two executed SQL Queries differ a lot. If I change InheritanceType.JOINED to InheritanceType.SINGLE_TABLE the first example works again.

Is this the expected behavior of InheritanceType.JOINED and EntityManager.find that I have to pass the superclass there ?

Thank you, frobb

---- sql trace from example 1 ----

Code:

DEBUG [SQL]: select dmsuser0_.id as id0_0_, dmsuser0_1_.name as name0_0_, dmsuser0_.password as password1_0_, dmsuser0_.groupName as groupName1_0_, dmsuser0_.description as descript4_1_0_ from DmsUser dmsuser0_ inner join Owner dmsuser0_1_ on dmsuser0_.id=dmsuser0_1_.id where dmsuser0_.id=?

---- sql trace from example 2 ----

Code:

DEBUG [SQL]: select owner0_.id as id0_0_, owner0_.name as name0_0_, owner0_1_.password as password1_0_, owner0_1_.groupName as groupName1_0_, owner0_1_.description as descript4_1_0_, case when owner0_1_.id is not null then 1 when owner0_2_.id is not null then 2 when owner0_.id is not null then 0 end as clazz_0_ from Owner owner0_ left outer join DmsUser owner0_1_ on owner0_.id=owner0_1_.id left outer join USER_GROUP owner0_2_ on owner0_.id=owner0_2_.id where owner0_.id=?

emmanuel · **Posted:** Wed Jul 26, 2006 3:14 pm

did you save the object using hibernate? your DB data are probably screwed up

frobb01 · **Joined:** Wed Jul 26, 2006 7:17 am **Posts:** 7

Hello, i used Hibernate to persist the object. I boiled it down to the following test lines:

Test model classes:

Code:

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class AbstractSuperclass{
    Long id;
    @Id @GeneratedValue
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
}

@Entity
public class Subclass extends AbstractSuperclass {}

Test Code:

Code:

   
        EntityManager firstSession = EntityManagerHelper.createSession();
        Subclass u = new Subclass();
        firstSession.getTransaction().begin();
        firstSession.persist(u);
        firstSession.getTransaction().commit();
        Long newId = u.getId();
        System.out.println("new ID is:" + newId);
        firstSession.close();

        EntityManager secondSession = EntityManagerHelper.createSession();
        secondSession.getTransaction().begin();

        // 1.
        Subclass result1 = secondSession.find(Subclass.class, newId);
        System.out.println("result is:" + result1);

        // 2.
        Subclass result2 = (Subclass) secondSession.find(AbstractSuperclass.class, newId);
        System.out.println("result is:" + result2);

        secondSession.getTransaction().commit();
        secondSession.close();

        EntityManagerHelper.shutdown();

Result is:

Code:

new ID is:1
result is:null
result is:com.riacom.dms.model.Subclass@3afb99

But it works (first result is != null) with SINGLE_TABLE. I think it may be a bug, should it be reported? Is there more information i should provide?

Frobb

emmanuel · **Posted:** Fri Jul 28, 2006 2:19 pm

attach a runnable version of your unit test case (please remove the helper class), and post it to JIRA. Also be sure that Subclass is actually part of the EMF creation

Thanks

frobb01 · **Joined:** Wed Jul 26, 2006 7:17 am **Posts:** 7

Something interesting I found out:

The code works for JOINED subclasses for Hsqldb and Postgres, but fails for MySql. So changing my database to postgres solves the problem for me.
I added a bug report containing the test case ejb-208.

Frobb