<?php
function generate_auto_increment_id($namespace, array $option = array())
    $option += array(
        'init' => 1,
        'step' => 1,
    $instance = new Mongo();
    $instance = $instance->selectCollection('_seq', 'seq');
    $seq = $instance->db->command(array(
        'findAndModify' => 'seq',
        'query'         => array('_id' => $namespace),
        'update'        => array('$inc' => array('id' => $option['step'])),
        'new'           => true,
    if (isset($seq['value']['id'])) {
        return $seq['value']['id'];
    $instance->insert(array(
        '_id' => $namespace,
        'id'  => $option['init'],
    return $option['init'];