I have a table with a composite Id of two fields, one autogenerated and one Foreign Key. In the Entity class I have the following Code:

@Entity
@Table(name = "personascambios")
public class PersonasCambios implements Serializable {
    private static final long serialVersionUID = 1L;
    @EmbeddedId
    protected PersonasCambiosPK personasCambiosPK;
    @Basic(optional = false)
    @Column(name = "activo")
    private short activo;
    @Basic(optional = false)
    @Column(name = "dt_afecta")
    @Temporal(TemporalType.TIMESTAMP)
    private Date dtAfecta;
    @Basic(optional = false)
    @Column(name = "usu_afecta")
    private String usuAfecta;
    @JoinColumn(name = "idPersona", referencedColumnName = "idPersona", insertable = false, updatable = false)
    @ManyToOne(optional = false)
    private Personas personas;

And in the Id Class I have the following code:

@Embeddable
public class PersonasCambiosPK implements Serializable {
    @Basic(optional = false)
    @Column(name = "idPersonaCambio")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private long idPersonaCambio;
    @Basic(optional = false)
    @Column(name = "idPersona")
    private long idPersona;

It's that the right way to declare the autogenerated field? How should I persist the PersonasCambios entity? I create a new PersonasCambiosPK object, and set the idPersonaCambio to 0L, and the idPersona to an id obtained from de DB, it works the first time, but when I want to persist a new PersonasCambios using the same idPersona, the application throws an Entity Exists Exception.

Thanks for your help in advance.