self-reference field mapping in JPA

Question

Lets say we have User entity class. User can be friends with other users. How can i map this self-reference collection field without creating a new entity called Connection or creating multiple entries in the database?

@Entity
public class User {
...
@ManyToMany
private Collection<User> friends;
...
}

USER_ID-FRIEND_ID
1 - 2
2 - 1 (duplicate... I don't need it)

Answer 1

Following is snapshot from my code for ElementEntity:

@OneToMany(mappedBy = "parent", fetch = FetchType.LAZY)
private List<ElementEntity> children;

@JoinColumn(name = "ParentId", referencedColumnName = "ElementId")
@ManyToOne(fetch = FetchType.LAZY)
private ElementEntity parent;

Where on database there are fields:

• ElementId - primary key;
• ParentId relation with parent