public function autoincrement($cb, $plain = false)
{
$e = explode('.', $this->name);
$col = (isset($e[1]) ? $e[0] . '.' : '') . 'autoincrement';
$this->pool->{$col}->findAndModify(['query' => ['_id' => isset($e[1]) ? $e[1] : $e[0]], 'update' => ['$inc' => ['seq' => 1]], 'new' => true, 'upsert' => true], $plain ? function ($lastError) use($cb) {
$cb(isset($lastError['value']['seq']) ? $lastError['value']['seq'] : false);
} : $cb);
}