Hibernate Inheritance SingleTable Subclass Joins

Question

Ive been working with Hibernate since a couple of weeks. Well its a very helpful tool but i cannot resolve following task:

Table:

Create Table `Product`
( 
  `product_id` INT(10) PRIMARY KEY, 
  `bundle_id` INT(10) NULL,
  `product_type` VARCHAR(50) NOT NULL,
  `title` VARCHAR(255) NOT NULL,
  `desc` VARCHAR(255) NULL, 
  `price` REAL(10) NOT NULL,
  ...
);

in Java i have 3 Classes

    @Entity
    @Table(name = "Product")
    @DiscriminatorColumn(name = "product_type")
    public abstract class Product {
        ...
    }

there are two types of instances, where an "Item" could but may not always deserve to a "Bundle". "Bundles" have at least one "Item"

    @Entity
    @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
    @DiscriminatorValue(value = "Item")
    public class Item extends Product {
        Bundle bundle;
        ....
        @ManyToOne (fetch=FetchType.LAZY, targetEntity=Bundle.class)
    @JoinColumn (name="bundle_id")
        public Bundle getBundle() {...}
        public void setBundle(Bundle bundle) {...}
        ....
    }

and:

    @Entity
    @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
    @DiscriminatorValue(value = "Bundle")
    public class Bundle extends Product {
        Set<Item> items;
        ....
        @OneToMany (mappedBy="bundle", targetEntity=Item.class)
    @OrderBy ("list_nr")
    public Set<Item> getItems() {...}
        public void setItems(Set<Item> items) {...}
        ....
    }

At Runtime its not possible to call any data, error: Expected type: org.blah.Bundle, actual value: org.blah.Item

does anyone have an idea or hint. isearching google up&down but i cannot find this specific issue.

Dont know why Hibernate try this:

Hibernate: 
select
    item0_.item_id as product1_7_,
    item0_1_.price as price3_7_,
    item0_1_.title as title4_7_,
    item0_.bundle_id as bundle3_11_
from
    Item item0_ 
inner join
    Product item0_1_ 
        on item0_.item_id=item0_1_.product_id

Error:

01.09.2013 00:36:49 org.hibernate.property.BasicPropertyAccessor$BasicSetter 
set ERROR: HHH000123: IllegalArgumentException in class: org.blah.Item, 
setter method of property: bundle 01.09.2013 00:36:49
org.hibernate.property.BasicPropertyAccessor$BasicSetter set ERROR: HHH000091: 
Expected type: org.blah.Bundle, actual value: org.blah.Item 01.09.2013 00:36:49    
org.blah.QueryMngr findAllItems SEVERAL: get failed

findAllItems():

public static List<Item> findAllItems() {
    log.debug("find all Item instances");
    Session session = null;
    try {
        session = HibernateUtil.getSessionFactory().openSession();
        session.getTransaction().begin();
        List<Item> items = session.createQuery("From Item").list();
        //for (Item item : items) {
        //  Hibernate.initialize(item.getBundle());
        //}
        session.getTransaction().commit();
        log.debug("get successful");
        session.close();
        return items;
    } catch (HibernateException exc) {
        if (session != null) {
            session.getTransaction().rollback();
            session.close();
        }
        log.error("get failed", exc);
        throw new RuntimeException( exc.getMessage() );
    }
}

Answer 1

In Bundle class change from

@OneToMany (mappedBy="bundle", targetEntity=Bundle.class)

to

@OneToMany (mappedBy="bundle", targetEntity=Item.class)

or remove parameter targetEntity at all.

From Hibernate documentation:

@ManyToOne has a parameter named targetEntity which describes the target entity name. You usually don't need this parameter since the default value (the type of the property that stores the association) is good in almost all cases. However this is useful when you want to use interfaces as the return type instead of the regular entity.