@Entity
@Table(name = "PARTICIPANT")
public class Participant implements Serializable {
    private static final long serialVersionUID = 1L;

    @EmbeddedId
    private ParticipantId id;

    public ParticipantId getId() {
        return id;
    }

    public void setId(ParticipantId id) {
        this.id = id;
    }
}

@Embeddable
public class ParticipantId implements Serializable {

    private static final long serialVersionUID = 1L;

    @Embedded
    @AttributeOverrides({
            @AttributeOverride( name = "registrationIndex", column = @Column(name = "REGISTRATION_INDEX")),
            @AttributeOverride( name = "registrationDisplay", column = @Column(name = "REGISTRATION_INDEX", insertable=false, updatable=false)),
    })
    private ParticipantRegistration registrationNumber;

    public ParticipantRegistration getRegistrationNumber() {
        return registrationNumber;
    }

    public void setRegistrationNumber(ParticipantRegistration registrationNumber) {
        this.registrationNumber = registrationNumber;
    }
}

@Embeddable
public class ParticipantRegistration implements Serializable {

    private static final long serialVersionUID = 1L;

    private String registrationIndex;

    private String registrationDisplay;

    public String getRegistrationIndex() {
        return registrationIndex;
    }

    public void setRegistrationIndex(String registrationIndex) {
        this.registrationIndex = registrationIndex;
    }

    public String getRegistrationDisplay() {
        return registrationDisplay;
    }

    public void setRegistrationDisplay(String registrationDisplay) {
        this.registrationDisplay = registrationDisplay;
    }
}