/// <summary>
    /// Checks if ch_deleted_messages already exist in database
    /// </summary>
    /// <param name="del_msg"></param>
    /// <returns>return true if ch_deleted_messages is exist in database. false if not exist.</returns>
    public static bool IsExist(ch_deleted_messages del_msg)
    {
        string queryIsExist = "SELECT COUNT(msg_id) FROM ch_deleted_messages WHERE msg_id=" + del_msg.msg_Id + " AND usr_id=" + del_msg.usr_Id;
        int    k            = Convert.ToInt32(Connect.MathAction(queryIsExist, "ch_deleted_messages"));

        if (k > 0)
        {
            return(true);
        }

        return(false);
    }
    /// <summary>
    /// Adds a new record of deleted message to the database.
    /// </summary>
    /// <param name="del_msg">the message to delete</param>
    /// <returns>true if the message deleted now. false if already deleted in the past.</returns>
    public static bool Add(ch_deleted_messages del_msg)
    {
        if (IsExist(del_msg))
        {
            return(false);
        }

        string strSql = "INSERT INTO ch_deleted_messages(msg_id, usr_id) ";

        strSql += "VALUES(" + del_msg.msg_Id + ", " + del_msg.usr_Id + ")";
        Connect.DoAction(strSql, "ch_deleted_messages");

        return(true);
    }
    protected void btnMsgSentDelete_Click(object sender, ImageClickEventArgs e)
    {
        string[] arr = hfSelectedRowsSent.Value.Split(',');
        for (int i = 0; i < arr.Length; i++)
        {
            if (Convert.ToInt32(arr[i]) >= 0)
            {
                GridViewRow current = gvMessagesSent.Rows[Convert.ToInt32(arr[i])];

                ch_deleted_messages del_msg = new ch_deleted_messages(Convert.ToInt32(((Label)current.FindControl("lbl_msg_id_sent")).Text), Convert.ToInt32(Session["usr_id"]));
                ch_deleted_messagesSvc.Add(del_msg);
            }
        }
        hfSelectedRowsSent.Value = "-1";

        //bind data
        GVBindSent();

        //select checkboxes
        SelectCheckboxesSent();
    }