JPA cascade actions on one-to-one relationship

I have the following question regarding one to one relationships (and I guess one to many also):

Let’s suppose I have the following tables:

create table user (
    id bigint auto_increment primary key,
    username varchar(100) not null,
    constraint UK_username unique (username)
);

create table user_details(
    userId bigint not null primary key,
    firstName varchar(100) null,
    lastName  varchar(100) null,
    constraint user_details_user_id_fk foreign key (userId) references user (id)
);

As you can see the two tables share the same primary key. Now the entities I created are the following:

import lombok.Data;

import javax.persistence.*;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.Size;

@Data
@Entity
public class User {

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

    @NotBlank
    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String username;

    @MapsId
    //without this I get an exception on this table not having a column named: userDetails_userId
    @JoinColumn(name = "id")
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private UserDetails userDetails;
}

import lombok.Data;

import javax.persistence.*;
import javax.validation.constraints.Size;

@Data
@Entity(name = "user_details")
public class UserDetails {

    @Id
    private Long userId;

    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String firstName;

    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String lastName;

}

When I try to persist a new user I have a user object with all the values generated except of the user.id and the userDetail.userId. When I try to persist this the error I get is the following:

"org.springframework.orm.jpa.JpaSystemException: ids for this class must be manually assigned before calling save(): com.app.entity.UserDetails; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.app.UserDetails

Note that to save a User entity I created this interface:

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

and I use the save method provided.

    ...

    @Autowired
    private UserRepository userRepository;

    ...

    public ResponseEntity<HttpStatus> addUser(User user) {
        userRepository.save(user);
        return ResponseEntity.ok(HttpStatus.OK);
    }

the object before saving looks like this:

User(id=null, username=test, userDetails=UserDetails(userId=null, firstName=test, lastName=test))

I was wondering if I can simply save a user object and cascade the generated key to the userDetail.

Should I use another approach for saving or there is something wrong with my entities?

Answer

You’ve done things from the wrong direction.

@Data
@Entity
public class User {

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

    @NotBlank
    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String username;

    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "user")
    private UserDetails userDetails;
}

@Data
@Entity(name = "user_details")
public class UserDetails {

    @Id
    private Long userId;

    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String firstName;

    @Column(unique = true)
    @Size(min = 1, max = 100)
    private String lastName;

    @MapsId
    @JoinColumn(name = "USERID")
    @OneToOne(fetch = FetchType.LAZY)
    private User user;
}

With this, you can just set the userDetail.user reference and JPA will persist both the user, assign it a ID and use that to populate the UserDetail.id value for you – in your model and in the database.

You should maintain the user.userDetail reference, but it is less consequential to the database row data and more for object consistency reasons.