Spring Boot Data Rest JPA：@ManyToOne未填充数据库中的ForeignKey列

Question

I am using Spring Boot Data Rest with JPA in TomCat to persist data in MySQL.

The problem: When a JSON to add a User is sent to the Rest endpoint, both MySQL tables are updated, BUT the values in the mapping column (phone.user_id) are set to 'NULL' (should be set to the corresponding User.uid)... What is missing from the code to work as intended ?

The resulting SQL tables and values:

// "user" table                  // "phone" table
uid | first_name                 pid | number   | user_id
----------------                 ------------------------
1   | John                       1   | 03432453 | NULL    <--- should show 1
                                 2   | 02451254 | NULL    <--- should show 1

The @OneToMany side:

@Entity    
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long uid;
    private String firstName;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="user", orphanRemoval=true)  
    private List<Phone> phones;

    /* getters and setters */

    public void addPhone(Phone phone) {
        this.phones.add(phone);
        phone.setUser(this);
    }

    /* UPDATED - method added */
    public User updatePhoneUserId(User user) {
        List<Phone> phs = user.getPhones();
        for (Phone ph : phs ) {
            ph.setUser(user);
        }
        return user;
     }
 }

The @ManyToOne side:

@Entity
public class Phone {

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

    private String number;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="user_id")
    private User user;

    /* getters and setters*/  

}

The UserRepository and PhoneRepository:

public interface UserRepository extends JpaRepository<User, Long> { }
public interface PhoneRepository extends JpaRepository<Phone, Long> { }

The Rest controller:

@RestController  
@RequestMapping(path="/api")
public class UserController {

    @Autowired 
    private UserRepository ur;

    @PostMapping(path="/add")
    public @ResponseBody String addNewUserPost(@RequestBody User user) {
        // ur.save(user);                       /* UPDATED - line removed */ 
        ur.save(user.updatePhoneUserId(user));  /* UPDATED - line added */

        return "Saved";
    }
}

Answer 1

After saving user to database repository model returns user object with updated values such as id.

So just do the following:

user = ur.save(user);

So user object will be replaced with the object that repository returns and id is not null anymore.