public static function dynColExpression($attrs) {
        if (!$attrs) {
            return null;
        }

        $params = [];

        // todo For now we only have Maria. Add PgSQL and generic JSON.
        static::encodeArrayForMaria($attrs);
        $sql = static::dynColSqlMaria($attrs, $params);

        return new \yii\db\Expression($sql, $params);
    }