How to define Friendship relationship using Hibernate?

Question

I need to have "FriendRequest" and "ListOfFriends" functionalities.Similar to facebook, which shows number of received friend requests and number of approved friends.

By "FriendRequest", I mean to have a list of friend requests that the user receives.

By "ListOfFriends", I mean to have a list of friends of the user.

To achieve that, I defined following class but when I try to retrieve a user using its username, a "Stackoverflow" exception message will be thrown. It seems it goes into an indefinite loop.

When I remove "FriendRequests" and "Friends" from my toString method it stops throwing the exception.

This question is similar to what I am going to achieve but the difference is I do not what to have a separate Credential class.

Member

@Entity
public class Member implements Serializable {
    @Id
    @GeneratedValue
    private long id;
    @Column(name = "username", nullable = false, unique = true)
    private String username;
    @Column(nullable = false)
    private String fname;
    @Column(nullable = false)
    private String lname;
    @OneToMany(fetch = FetchType.EAGER, mappedBy = "requester")
    private Set<Friendship> friendRequests = new HashSet<Friendship>();
    @OneToMany(fetch = FetchType.EAGER, mappedBy = "friend")
    private Set<Friendship> friends = new HashSet<Friendship>();

    getters and setters

    @Override
    public String toString() {
       return "Member [
                .....                 
                , fname=" + fname + ", lname=" + lname
                //  + friendRequests.size() + ", friends=" + friends.size() + 
       "]";
    }
}

Friendship

@Entity
public class Friendship implements Serializable {
    @Id
    @ManyToOne
    @JoinColumn(referencedColumnName = "username")
    Member requester;
    @Id
    @ManyToOne
    @JoinColumn(referencedColumnName = "username")
    Member friend;
    @Temporal(javax.persistence.TemporalType.DATE)
    Date date;
    @Column(nullable = false)
    boolean active;

Answer 1

I would like to suggest DB Design.

Right now, You are having a friendship table and friends table as per POJO classes. Instead of that, you can just only have friendship table with one more column boolean isAccepted;(variable in POJO class).

If boolean value is true, It means that that member(friend) is a friend. When you want to get all the friends, retrieve the rows of friendship with isAccepted set to true; If you want to get only friendrequests(Or pending requests to be Approved), get all the rows with isAccepted set to false.

With the present DB design or ER model, you are using. You need to delete the row from the friendship table (as It is no more a friend request), If the person accepts the friend request and store somewhere. Where do you store the friends . According to your present design, It stores in the friends table. But there is no column saying that the row indicates a friend of someone. It is just like adding a row(friend) to the friends table every time one member accepts the request of other member and just making redundant rows.