@Entity
@Table(uniqueConstraints = @UniqueConstraint(columnNames = "cpf"))
public class Cliente {
...
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "cliente_id")
private Long codcli;

@OneToMany(mappedBy = "clienteAssociado", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<Cartao> cartoes;
...
}

@Entity
public class Cartao{
...
@ManyToOne
@JoinColumn(name = "cliente_id")
private Cliente clienteAssociado;
...
}

<Clientes>
  <Cliente> <!-- I can have many 'cliente' in the file -->
  ... Atributes
  <Cartoes>
    <Cartao> <!-- I can have many 'cartao' in the file -->
    ...Atributes
    </Cartao>
  </Cartoes>
  </Cliente>
</Clientes>

SELECT * FROM CLIENTE;
CLIENTE_ID      CPF     IDADE   NOME        SEXO
1               value   value   value       value
2               value   value   alue        value

SELECT * FROM CARTAO;
CARTAO_ID   BANDEIRA    LIMITE      SEGMENTO    CLIENTE_ID
1           value        value       value        null <- Here is my problem
2           value        value       value        null
3           value        value       value        null