Cascading of persist, does not create identifiaction-CodePudding

Having this entities:

User.java:

@Entity
@NoArgsConstructor
@Getter
@Setter
public class User {
    @Id @GeneratedValue
    private Long id;
    private String username;
    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @MapKey(name = "friend_id")
    private Map<User, Friendship> friends = new HashMap<>();
}

Friendship.java:

@Entity
@Data
@IdClass(Friendship.class)
public class Friendship implements Serializable {
    @Id
    private Long owner_id;
    @Id
    private Long friend_id;
    private String level;
    @ManyToOne(cascade = CascadeType.ALL)
    @MapsId("owner_id")
    private User owner;
    @ManyToOne(cascade = CascadeType.ALL)
    @MapsId("friend_id")
    private User friend;
}

and DemoApplication.java:

@Bean
    public CommandLineRunner loadData(UserRepository userRepo){
        return new CommandLineRunner() {
            @Override
            public void run(String... args) throws Exception {
                User owner = new User();
                owner.setUsername("owner");
                User f1 = new User();
                f1.setUsername("f1");
                User f2 = new User();
                f2.setUsername("f2");
                Friendship fs1 = new Friendship();
                fs1.setOwner(owner);
                fs1.setFriend(f1);
                Friendship fs2 = new Friendship();
                fs2.setOwner(owner);
                fs2.setFriend(f2);
                owner.getFriends().put(f1, fs1);
                owner.getFriends().put(f2, fs2);
                userRepo.saveAndFlush(owner);
            }
        };
    }

I get error:

A different object with the same identifier value was already associated with the session : [com.example.demo.model.Friendship#Friendship(owner_id=null, friend_id=null, level=null, owner=com.example.demo.model.User@2b036135, friend=com.example.demo.model.User@a9e28af9)]

Which means both Users f1 and f2, are having null in Long id. The indeed have, when the object is created, but I thought the mapping had specified CascadeType.ALL and @GeneratedValue so the if should be created.

But I had try to set the ids myself:

            ...
            f1.setUsername("f1");
            f1.setId(1L);
            User f2 = new User();
            f2.setUsername("f2");
            f2.setId(2L);
            ...

But now I got

detached entity passed to persist: com.example.demo.model.User

So I guess I should let the creation of primary keys on JPA. But as you saw from above, it does not that even with Cascading. So what now?

CodePudding user response：

In your User entity @Id @GeneratedValue create column with Primary key but not with Auto Increment and while you insert data manually inside id column it produce error, because it is Primary key...

Change:

@Id @GeneratedValue

To:

@Id @GeneratedValue(strategy = GenerationType.IDENTITY)

For auto increment

CodePudding user response：

Try adding this under your @Id annotation

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)