(PECL mongo >= 1.0.2)
MongoMaxKey is an special type used by the database that compares greater than all other possible BSON values. Thus, if a query is sorted by a given field in ascending order, any document with a MongoMaxKey as its value will be returned last.
MongoMaxKey has no associated fields, methods, or constants. It is merely the "greatest" value that can be represented in the database.
Note: MongoMaxKey is used internally by MongoDB for indexing and sharding. There is generally no reason to use this class in an application.
$collection->insert(array("task" => "dishes", "doBy" => new MongoMaxKey));
$collection->insert(array("task" => "staff meeting", "doBy" => new MongoDate(strtotime("+4 days"))));
$cursor = $collection->find()->sort(array("doBy" => 1));
The cursor will return the staff meeting document followed by the dishes document. The dishes document will always be returned last, regardless of what else is added to the collection (unless other documents are added with MongoMaxKey in their "doBy" field).