JPA merge parent with new child

Question

I have the following structure (OneToOne unidirectional)

@Entity
public class Car {
    @Id
    @Column(name = ID)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToOne(fetch = FetchType.EAGER, cascade = { CascadeType.ALL }, orphanRemoval = true )
    @JoinColumn(name = "DRIVER_ID")
    private Driver driver;

    // setters and getters and other properties
}

@Entity
public class Driver {
    @Id
    @Column(name = ID)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    // setters and getters and other properties
}

The problem is, that if I already have an existing Car, but no driver and I add a driver to the queried Car from the database, the Driver will get inserted (I see the insert query generated).

The following logic happens inside a transaction:

// this is a raw version of the code that gets executed, skipped validation and stuff like that
public void addDriver(long carId, Driver driver) {
    entityManager.persist(driver);
    Car car = entityManager.find(Car.class, carId);
    car.setDriver(driver);
}

After the transaction is finished, I query the car, but the car doesn't have a driver attached. Any idea why this is happening and how can this be fixed?

Answer 1

If you're relying on your entity existing in the database after your call to persist(), but before the transaction commits, then call flush() first.

Refer this for details:

http://blakecaldwell.net/blog/2013/9/3/dont-rely-on-entitymanagerpersist-for-immediate-insert.html

Answer 2

And if you try

public void addDriver(long carId, Driver driver) {
Car car = entityManager.find(Car.class, carId); car.setDriver(driver); entityManager.merge(car) }

Because you are cascading the car should be inserted and linked.