Hoping someone can help.

I have an app that I'm trying to use EJB3 entities for.

One entity represents a Person:

@Entity
@Table (name = "USERS")
@Inheritance (strategy = InheritanceType.JOINED)
public class Person {

    @Column (name = "PERSON_ID")
    @Id
    @SequenceGenerator (name = "personIdGenerator", allocationSize = 1, sequenceName = "PERSON_SEQ")
    @GeneratedValue (generator = "personIdGenerator", strategy = GenerationType.SEQUENCE)
    private long id;

   @Column (name = "EMAIL")
   private String email;
    
    @Column (name = "FIRSTNAME")
    private String firstName;
    
   @Column (name = "LASTNAME")
   private String lastName;

   ...
}

Now I have another entity called PrimaryInvestigator that extends Person so I can use the email, lastname, firstname attributes.  However the db table for this entity has a composite key representing the person's id and the project the person is associated with: projectId.  So this entity requires a composite key.  :

@Entity
@IdClass (PrimaryInvestigatorPK.class)
@Table (name = "PROJECT_PI")
public class PrimaryInvestigator extends Person {

    @Column (name = "PROJECT_ID", insertable=false, updatable=false)
    @Id
    private long projectId;

    @Column (name = "BIOSKETCH_FILE_ID") 
    private long biosketchFileId;
    ...
}

My IdClass for the PrimaryInvestigator entity looks like this:

public class PrimaryInvestigatorPK implements Serializable {

  public Long userId;
  public Long projectId;

  ...
}

Since part of the composite key is in the Person superclass, I figured I could just add another @Id attribute representing the other part of the composite key and Hibernate would simply use the combination of the two in my composite key.

However, every time I try to deploy the EJBs, I get the following exception:

 org.hibernate.AnnotationException: Unable to define/override @Id(s) on a subclass: org.jlab.mis.apps.mics.valueobjects.PrimaryInvestigator

Is what I'm trying to do possible?  If so how? 

I can't use a @MappedSuperclass because I need to be able to persist Person objects by themselves...

Any ideas?