@Entity
@Table(name = "groups")
public class Group implements Serializable {

    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    @Column(name = "name")
    private String name;
}

@SqlResultSetMapping(
        name = "user_result",
        entities = @EntityResult(
                entityClass = User.class,
                fields = {
                    @FieldResult(name = "id", column = "id"),
                    @FieldResult(name = "name", column = "name"),
                    @FieldResult(name = "group.id", column = "group_id"),
                    @FieldResult(name = "group.name", column = "group_name")}))
@NamedNativeQuery(
        name = "Usuario.findAll",
        query = "SELECT u.id, u.name, u.group_id, g.name AS group_name FROM users u INNER JOIN groups g ON u.group_id = g.id",
        resultSetMapping = "user_result")
@Entity
@Table(name = "users")
public class User implements Serializable {

    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    @Column(name = "name")
    private String name;
    @ManyToOne
    @JoinColumn(name = "group_id", referencedColumnName = "id")
    private Group group;