public class Customer {

  @Id
  @GeneratedValue
  private Long id;

  private String name;
  private Integer age;

  @OneToMany(mappedBy = "customer")
  List<CustomerOrder> customerOrders;

}

public class Product {

  @Id
  @GeneratedValue
  private Long id;
  private String name;
  private BigDecimal price;

  @ToString.Exclude
  @EqualsAndHashCode.Exclude
  @OneToMany(mappedBy = "product")
  List<CustomerOrder> customerOrders;
}

public class CustomerOrder {

  @Id
  @GeneratedValue
  private Long id;
  private String description;
  private Integer quantity;

  @ManyToOne(cascade = CascadeType.PERSIST)
  @JoinColumn(name = "customer_id")
  private Customer customer;

  @ManyToOne()
  private Product product;

}