MONGODBREF(3) 1 MONGODBREF(3)
The MongoDBRef class
INTRODUCTION
This class can be used to create lightweight links between objects in different collections.
Motivation: Suppose we need to refer to a document in another collection. The easiest way is to create a field in the current document. For
example, if we had a "people" collection and an "addresses" collection, we might want to create a link between each person document and an
address document:
Example #1
Linking documents
<?php
$people = $db->people;
$addresses = $db->addresses;
$myAddress = array("line 1" => "123 Main Street",
"line 2" => null,
"city" => "Springfield",
"state" => "Vermont",
"country" => "USA");
// save the address
$addresses->insert($myAddress);
// save a person with a reference to the address
$me = array("name" => "Fred", "address" => $myAddress['_id']);
$people->insert($me);
?>
Then, later on, we can find the person's address by querying the "addresses" collection with the MongoId we saved in the "people" collec-
tion.
Suppose now that we have a more general case, where we don't know which collection (or even which database) contains the referenced docu-
ment. MongoDBRef is a good choice for this case, as it is a common format that all of the drivers and the database understand.
If each person had a list of things they liked which could come from multiple collections, such as "hobbies", "sports", "books", etc., we
could use MongoDBRefs to keep track of what "like" went with what collection:
Example #2
Creating MongoDBRef links
<?php
$people = $db->selectCollection("people");
// model trains are in the "hobbies" collection
$trainRef = MongoDBRef::create("hobbies", $modelTrains['_id']);
// soccer is in the "sports" collection
$soccerRef = MongoDBRef::create("sports", $soccer['_id']);
// now we'll know what collections the items in the "likes" array came from when
// we retrieve this document
$people->insert(array("name" => "Fred", "likes" => array($trainRef, $soccerRef)));
?>
Database references can be thought of as hyperlinks: they give the unique address of another document, but they do not load it or automat-
ically follow the link/reference.
A database reference is just a normal associative array, not an instance of MongoDBRef, so this class is a little different than the other
data type classes. This class contains exclusively static methods for manipulating database references.
CLASS SYNOPSIS
MongoDBRef
MongoDBRef
Methods
o publicstatic array MongoDBRef::create (string $collection, mixed $id, [string $database])
o publicstatic array MongoDBRef::get (MongoDB $db, array $ref)
o publicstatic bool MongoDBRef::isRef (mixed $ref)
SEE ALSO
MongoDB core docs on databases references.
PHP Documentation Group MONGODBREF(3)
