public function globalFilter()
    {
        $globalSearch = [];
        if (isset($this->request['search']) && !empty($this->request['search']['value'])) {
            for ($i = 0, $ien = count($this->request['columns']); $i<$ien; $i++) {
                if (self::isSearchable($this->columns[$i])) {
                    $where_condition = $this->toSQLColumn($this->columns[$i], 2).' LIKE '.$this->pdoLink->quote('%'.$this->request['search']['value'].'%');
                    if (!$this->setHaving($where_condition, $this->columns[$i])) {
                        $globalSearch[] = $where_condition;
                    }
                }
            }
        }

        return empty($globalSearch) ? '' : '('.implode(' OR ', $globalSearch).')';
    }