The MongoDBRef class

(PECL mongo >=0.9.0)


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:

Exemplo #1 Linking documents


$addresses $db->addresses;

$myAddress = array("line 1" => "123 Main Street"
"line 2" => null,
"city" => "Springfield",
"state" => "Vermont",
"country" => "USA");

// save the address

// save a person with a reference to the address
$me = array("name" => "Fred""address" => $myAddress['_id']);


Then, later on, we can find the person's address by querying the "addresses" collection with the MongoId we saved in the "people" collection.

Suppose now that we have a more general case, where we don't know which collection (or even which database) contains the referenced document. 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:

Exemplo #2 Creating MongoDBRef links



// 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 automatically 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.

Sinopse da classe

MongoDBRef {
/* Métodos */
public static array create ( string $collection , mixed $id [, string $database ] )
public static array get ( MongoDB $db , array $ref )
public static bool isRef ( mixed $ref )

Veja Também

MongoDB core docs on » databases references.


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User Contributed Notes 1 note

jaimz at vertigolabs dot org
7 months ago
While you can create a DBRef object for a GridFS document, you CAN NOT load a document from GridFS using a DBRef.

This is dependent on the driver, not MongoDB.
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