<?php
$collection->insert(array("task" => "lunch", "do by" => new MongoMinKey));
$collection->insert(array("task" => "staff meeting", "do by" => new MongoDate(strtotime("+4 days"))));
$cursor = $collection->find()->sort(array("do by" => 1));
?>
The cursor will contain the lunch document, then the staff meeting document.
The lunch document will always be returned first, regardless of what else
is added to the collection (unless other documents are added with
MongoMinKey in the "do by" field).