private void Button_Click_Delete_Row(object sender, RoutedEventArgs e)
        {
            int id = (FriendsDataGrid.SelectedItem as user).user_id;

            FriendService friendService = new FriendService();

            using (SteamContext context = new SteamContext())
            {
                user tmp = (from user in context.Users where user.user_id == id select user).SingleOrDefault();

                friendService.DeleteFriends(tmp);
            }

            user user2 = new user()
            {
                user_id = 2, nickname = "EEE", register_date = new DateTime(1582, 10, 5), status_id = 1, IsDeleted = 0, password = "******", wallet_id = 1
            };

            var userFriends = friendService.GetUserFriends(user2);

            FriendsDataGrid.ItemsSource = userFriends;
        }