vaninh0,
you can only create owned relationships in the datastore if the
child's key is of type com.google.appengine.api.datastore.Key or
String ("Key as Encoded String").
Check this part of the documentation:
http://code.google.com/appengine/docs/java/datastore/creatinggettinganddeletingdata.ht
Ops, I posted with one mistake... correcting:
@Entity(name = "Usuario")
@Table(name = "usuario")
public class Usuario {
@Id
@Column(name = "id_usuario")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@ManyToOne(fetch = FetchType
