Question

I created relation @ManyToMany with the same entity.

Here is my entity:

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

...

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "table_friends", joinColumns =
@JoinColumn(name = "userId"), inverseJoinColumns =
@JoinColumn(name = "friendId"))
private List<User> friends;

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "table_friends", joinColumns =
@JoinColumn(name = "friendId"), inverseJoinColumns =
@JoinColumn(name = "userId"))
private List<User> friendsof;

I created a few “users” and added them to friend list:

User u1 = new User();
User u2 = new User();
User u3 = new User();

u1.getFriends().add(u2);
u1.getFriendsof().add(u2);
u1.getFriends().add(u3);
u1.getFriendsof().add(u3);

When I remove a friend from the list u1.getFriends().remove(u3), everything is ok . But when I want to delete the user from the database u3.remove(), friends of u1 still are the same, although already in the database list of friend is correct.

1. Can I somehow refresh the list after removing a user?
2. And if so, how can I know which list of friend I need to refresh?

Edit: Also seems to me that I should remove the (cascade = CascadeType.ALL), because when I remove u1, removes all paired members. Is this the correct behavior?

Answer 1

Hmm, why do you need 2 list friends and friendsOf? If you’re my friend, isn’t it obvious that I am your friend?

Besides, if you only want to end the relationship between 2 User, you should use u1.getFriends().remove(u3).

Lastly, if you want to remove a user. You should create an EntityManager em and execute the command em.remove(u3). This command will delete u3 as well as the relationship. However, you should be careful with cascade = CascadeType.ALL. This cascadeType means that if you remove u3, u1 will also be removed. I think you should leave it @ManyToMany without cascade.