@Entity
@Table(name = "users_rooms")
public class UserRoom {

    @EmbeddedId
    private UserRoomId id;

    @NotNull
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;
    public User getUser() { return user; }
    public void setUser(User user) { this.user = user; }

    @NotNull
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "room_id")
    private Room room;
    public Room getRoom() { return room; }
    public void setRoom(Room room) { this.room = room; }

    @Column(name = "notifications_muted")
    private boolean notificationsMuted;
    public boolean getNotificationsMuted() { return notificationsMuted; }
    public void setNotificationsMuted(boolean notificationsMuted) { this.notificationsMuted = notificationsMuted; }

    public UserRoom() {}
    public UserRoom(User user, Room room){
        this.user = user; this.room = room;
    }
}

@Embeddable
class UserRoomId implements Serializable{
    private Long user;
    private Long room;
}