(PECL mongo >= 0.9.0)
MongoDBRef::create — Creates a new database reference
If no database is given, the current database is used.
Collection name (without the database name).
The _id field of the object to which to link.
Returns the reference.
Example #1 MongoDBRef::create() example
This creates a database reference to a document in the addresses collection. The MongoCollection::getName() function returns the name of the collection (not including the database name).
$addresses = $db->addresses;
$people = $db->people;
// save $address so it has an _id
// create a reference
$ref = MongoDBRef::create($addresses->getName(), $address['_id']);
// set the field in $person
$person['address'] = $ref;