Raducu Raducu - 2 years ago 145
Java Question

MVC SpringBoot and JPA Relationship

I have an issue with the JPA relationship within a MVC SpringBoot application.

I'm trying to create an application where I have a number of users and every user can have a number of cars. A user can have multiple cars. I've done a @OneToOne relationship between the user and the car object, here's what I've done:

here is the User class:

@Entity
@Table(name = "user")
public class User implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

@Column(name = "username", nullable = false)
private String username;

@Column(name = "password", length = 500, nullable = false)
private String password;

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private List<Car> cars;

}


then here is the Car class:

@Entity
@Table(name = "car")
public class Car implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@Column(length = 11)
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

@Column(name = "make", nullable = false)
private String make;

@Column(name = "model", nullable = false)
private String model;

@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinColumn(name = "id")
private User user;

}


Then, here is the actual service implementation

@Component
@Transactional(readOnly = true)
public class CarServiceImpl implements CarService {

@Inject
private CarRepository carRepository;

@Inject
private UserRepository userRepository;

@Override
@Transactional(readOnly = false)
public Car addCar(Long userId, Car car) {
User user = userRepository.findOne(userId);
user.getGpsLocationModels().add(car);

car.setUser(user);
carRepository.save(car);

return car;
}


then I have the endpoint but that works fully. The add method looks like does work as supposed to, at least I get the expected output, however the find method I have no idea how to write it, well can't figure it out how to retrieve cars based on user, I know how to get them by their ID but not for every user separately.

Here is my try:

@Override
public Car findCar(Long userId, Long carId) {

//get the current user (that comes as JSON Request Param)
User user = userRepository.findOne(userId);

//get the car based on its ID, here's the problem, I want the car based on its ID AND its user, I can't display cars which aren't for that particular user
Car car = carRepository.findOne(carId);

return car;
}


Here is the method for get all cars for a particular user:

@Override
public List<Car> displayAllCars(Long userId) {
return userRepository.findOne(userId).getCars();
}


I'd really appreciate any help that you could advise.

Thank you so much

Answer Source

Your mappings are incorrect. Car > User is @ManyToOne. If you also make this bi-directional you can also then retrieve the cars via the user:

@Entity
@Table(name = "user")
public class User implements Serializable {

    @OneToMany(mappedBy ="user",cascade = CascadeType.ALL)
    private Set<Car> cars;

    public Set<Car> getCars(){
        return cars;
    }

    public void addCar(Car car){
        cars.add(car);
        car.setUser(this);
    }
}

@Entity
@Table(name = "car")
public class Car implements Serializable {

    @ManyToOne(fetch=FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name="user_id")
    private User user;
}

@Override
public Set<Car> findCars(Long userId) {
    return userRepository.findOne(userId).getCars();
}
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