protected function _get_table_info()
    {
        $this->table_info = array();
        $db = Fruit_db::get_instance($this->connection);
        $db->query("SHOW COLUMNS FROM `{$this->table}`");
        $this->table_info[$this->table] = $db->result();
        if ($this->join)
        {
            foreach ($this->join as $alias => $join)
            {
                $db->query("SHOW COLUMNS FROM `{$join['join_table']}`");
                $this->table_info[$alias] = $db->result();
            }
        }
        return true;
    }