hibernate - MappingException: Could not determine type; Using @Embeddable and @Embedded

Question

I am attempting to move a framework from hibernate3 to 4, this code worked in 3. The framework uses Interfaces to break the tight coupling of classes. Hence:

The Entity class is marked with @Entity and this instance uses and an instance of and @Embeddable defined as its interface, a very familiar pattern in Spring.

The code works fine in older versions of hibernate (V3), I am moving it to JPA2 and Hibernate 4

I realize that Hibernate would have a difficult time figuring out which implementation (concrete class) of the interface was being being mapped. Hence I understand the error, however, it does work on older versions.

Is this due to hibernate templates and mapping classes in older versions that are abstracted away in JPA2 & H4.

Is the best approach to simply create concrete implementations of all the interface implementing classes and define the @embedded as a concrete class.

Thanks much in advance.

// the Entity class HibAttribute

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
// Define a unique constraint on item, namespace, and localname
@Table(name="attribute", uniqueConstraints = {
        @UniqueConstraint(columnNames={"itemid", "namespace", "localname"})})
// Define indexes on discriminator and key fields
@org.hibernate.annotations.Table(
        appliesTo="attribute", 
        indexes={@Index(name="idx_attrtype", columnNames={"attributetype"}),
                 @Index(name="idx_attrname", columnNames={"localname"}),
                 @Index(name="idx_attrns", columnNames={"namespace"})})
@DiscriminatorColumn(
        name="attributetype",
        discriminatorType=DiscriminatorType.STRING,
        length=16)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)

public abstract class HibAttribute extends HibAuditableObject implements java.io.Serializable, Attribute {

    // Fields

    @Embedded
    @AttributeOverrides( {
            @AttributeOverride(name="namespace", column = @Column(name="namespace", nullable = false, length=255) ),
            @AttributeOverride(name="localName", column = @Column(name="localname", nullable = false, length=255) )
    } )
    private QName qname;


//  The interface public interface QName {

    /**
     * Get local name
     * @return local name
     */
    public String getLocalName();

    /**
     * Set local name
     * @param localName local name
     */
    public void setLocalName(String localName);

    /**
     * Get namespace
     * @return namespace
     */
    public String getNamespace();

    /**
     * Set namespace
     * @param namespace namespace
     */
    public void setNamespace(String namespace);

    /**
     * Create copy of QName object.
     * @return copy of current QName object
     */
    public QName copy();

}

@Embeddable
public class HibQName implements QName {

    public static final String DEFAULT_NAMESPACE = "org.osaf.cosmo.default";

    private String namespace = null;
    private String localName = null;

    public HibQName() {}

    /**
     * Create new QName with specified namespace and local name.
     * @param namespace namespace
     * @param localName local name
     */
    public HibQName(String namespace, String localName) {
        this.namespace = namespace;
        this.localName = localName;
    }

// rest of class has been omitted ....... it is not needed to understand this issue.

The Stack trace: Caused by: org.hibernate.MappingException: Could not determine type for: org.timbre.model.QName, at table: attribute, for columns: [org.hibernate.mapping.Column(attributes_KEY)] at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:304) at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:288) at org.hibernate.mapping.IndexedCollection.validate(IndexedCollection.java:90) at org.hibernate.cfg.Configuration.validate(Configuration.java:1294) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1732) at org.hibernate.ejb.EntityManagerFactoryImpl.(EntityManagerFactoryImpl.java:88) at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:904) ... 57 more