不能将元素添加到“一对多”关系中。

Question

I have the following problem: I am not able to add a new Car to the corresponding Customer entity. The error is the following:

Duplicate entry 'test_login' for key 'UK_l4t3rudi0h7ibnjpnbvcnkcbf'

where 'test_login' is the Customer login.

Here the code for the Customer entity

public class Customer{
    @Id
    @GeneratedValue
    @Column (name = "id")
    private int id;

    @Column (name = "login", nullable = false, unique = true)
    private String login;

    @OneToMany(mappedBy = "customer", cascade = CascadeType.ALL)
    private List<Vehicle> vehicles = new  ArrayList<>();

    public void addVehicle(Vehicle vehicle){
        vehicle.setCustomer(this);
        vehicles.add(vehicle);
    }
 }

For Vehicle entity

@Entity
@Table(name = "vehicle")
public class Vehicle implements Serializable {
    @Id
    @GeneratedValue
    @Column (name = "id")
    private int id;

    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "customer_id")
    private Customer customer;
}

DAO implementation class:

public void addANewVehicle(Vehicle vehicle, Customer customer) {

        customer.addVehicle(vehicle);
        Session session = sessionFactory.openSession();
        try {

            session.getTransaction().begin();
            session.save(customer);
            session.getTransaction().commit();

        } catch (Exception e) {
            session.getTransaction().rollback();
            logger.error("Error occurred while adding a new car. Error stack trace: " + e.toString());
        } finally {
            session.close();
        }

Answer 1

@Column (name = "login", nullable = false, unique = true)
private String login;

Field login is set to unique, when save customer without primary key hibernate will create insert statement and Field login will duplicate.

try to load customer and save it

public void addANewVehicle(Vehicle vehicle, Customer customer) {

    Session session = sessionFactory.openSession();
    try {

        session.getTransaction().begin();
        Customer cust = session.get(Customer.class,customer.getId());
        cust.addVehicle(vehicle);
        session.getTransaction().commit();

    } catch (Exception e) {
        session.getTransaction().rollback();
        logger.error("Error occurred while adding a new car. Error stack trace: " + e.toString());
    } finally {
        session.close();
    }