public function orWhere()
    {
        $operator = 'OR';
        // is the first time call where method ?
        if ($this->_where_str == '') {
            $this->_where_str = ' WHERE ';
        } else {
            $this->_where_str .= ' '.$operator.' ';
        }
        // build attribute, bind params
        $this->_condition_constructor(func_num_args(), func_get_args(), $this->_where_str);

        return $this;
    }