mongodb产生自增id代码

function get_autoincre_id($name, $db){
		$update = array('$inc'=>array("id"=>1));
		$query = array('table_name' => $name);
		$command = array(
			'findandmodify'=>'autoincre_system', 'update'=>$update,
			'query'=>$query, 'new'=>true, 'upsert'=>true
		);
		$id = $db->command($command);
		return $id['value']['id'];