public function sqlFilters()
    {
        if (!$this->hasFilters()) {
            return '';
        }

        $criteria = $this->createFilter([
            'filters' => $this->filters()
        ]);

        $sql = $criteria->sql();
        if (strlen($sql) > 0) {
            $sql = ' WHERE '.$sql;
        }

        return $sql;
    }