public static function getKeys($filter = []): array
    {
        /* @var $class LightModel */
        $className = get_called_class();
        $class = new $className;
        $tableKey = $class->getKeyName();

        $sql = 'SELECT ' . $tableKey . ' FROM ' . $class->getTableName() . ' WHERE 1=1';
        $params = self::handleFilter($sql, $filter, $class);

        $query = DB::getConnection()->prepare($sql);
        $query->execute($params);

        $res = [];

        foreach ($query->fetchAll() as $key => $value)
        {
            $res[] = $value[0];
        }

        return $res;
    }