5.5.15

The MongoId class

(PECL mongo >=0.8.0)

Introduction

A unique identifier created for database objects. If an object is inserted into the database without an _id field, an _id field will be added to it with a MongoId instance as its value. If the data has a naturally occuring unique field (say, a username or timestamp) it is fine to use this as the _id field instead, and it will not be replaced with a MongoId.

Instances of the MongoId class fulfill the role that autoincrementing does in a relational database: to provide a unique key if the data does not natually have one. Autoincrementing does not work well with a sharded database, as it is impossible to find what the next number should be quickly. This class fulfills the constraints of quickly generating a value that is unique across shards.

Each MongoId is 12 bytes (making its string form 24 hexidecimal characters). The first four bytes are a timestamp, the next three are a hash of the client machine's hostname, the next two are the two least significant bytes of the process id running the script, and the last three bytes are an incrementing value.

MongoIds are serializable/unserializable. Their serialized form is similar to their string form:

C:7:"MongoId":24:{4af9f23d8ead0e1d32000000}

Class synopsis

MongoId {
public string $id = NULL ;
/* Methods */
public __construct ([ string $id = NULL ] )
public static string getHostname ( void )
public int getInc ( void )
public int getPID ( void )
public int getTimestamp ( void )
public static bool isValid ( mixed $value )
public static MongoId __set_state ( array $props )
public string __toString ( void )
}

Fields

id
This field contains the string representation of this object.

See Also

MongoDB core docs on » ids.

Table of Contents

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User Contributed Notes 6 notes

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5
rmarscher
1 year ago
You can also cast the id to a string rather than access the $id property to get a string representation of the MongoId.

<?php
$stringId
= (string) $mongoId;
?>
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2
Lionel
1 year ago
Just to be careful with the strict comparison. Object inequalities holds.

<?php

$m1
= new MongoId('51b14c2de8e185801f000006');
$m2 = new MongoId('51b14c2de8e185801f000006');

var_dump($m1 === $m2); //gives you boolean false
var_dump($m1 == $m2); //gives you boolean true

$m3 = new MongoId('51b14c2de8e185801f000006');
$m4 = new MongoId('51b14c2de8e185801f000007');

var_dump($m3 === $m4); //gives you boolean false
var_dump($m3 == $m4); //gives you boolean false

?>
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2
alex dot turpin at gmail dot com
3 years ago
If you need to get the actual ID string, and you try the usual way, PHP will whine because it starts with a dollar sign and it thinks it's a variable. Instead, use this notation:

<?php
    $mongoid
->{'$id'} //Get the $id property of a MongoId object
?>
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1
georgedot dont spam me gmail caom
1 year ago
Due to Recent changes.

* [PHP-554] - MongoId should not get constructed when passing in an invalid ID.

Constructor will throw an exception when passing invalid ID.

<?php

$_id
= new MongoId(); //Generates new ID
$_id = new MongoId(null); //Generates new ID

$_id = new MongoId("invalid id"); //throws MongoException

?>

<?php
//Revert to old behaviour
$_id = "invalid id";
try {
   
$_id = new MongoId($_id);
} catch (
MongoException $ex) {
   
$_id = new MongoId();
}
?>

<?php
//Nifty hack
class SafeMongoId extends MongoId {

    public function
__construct($id=null) {

        try {
           
parent::__construct($id);
        } catch (
MongoException $ex) {
           
parent::__construct(null);
        }

    }
}
?>
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1
Ryan S
1 year ago
it is important to note that

<?php
   
array("_id" => new MongoId("50cf7d2841d41f4f35000000"))
//                   ≠
   
array("_id" => array("$id" => "50cf7d2841d41f4f35000000"))
?>

This issue can arrise when using json_encode() and json_decode(). If not paying close enough attention one can assume due to the encoded value of the object that it is just this simple:

<?php
    $item
= $db->myCollection->findOne();
    print
json_encode($item);
   
// {"_id": {"$id": "50cf7d2841d41f4f35000000"}}
   
$item = $db->myCollection->findOne(json_encode($item));
   
// $item is empty aka not found
?>

Simple solution to handle these situations:

<?php
   
class MongoId2 extends MongoId {
        public function
__construct($id = null) {
            if(
is_array($id)) {
               
$id = (object) $id;
            }

            if(
is_object($id) && isset($id->{'$id'})) {
               
$id = $id->{'$id'};
            }

            return
parent::__construct($id);
        }
    }
?>
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0
sararschreiber at gmail dot com
3 years ago
this is useful for querying for an object by id, given the id's hex:

<?php
$userid
= '4cb4ab6d7addf98506010000';

$theObjId = new MongoId($userid);

$connection = new Mongo();
$db = $connection->thedb->users;

// this will return our matching entry.
$item = $db->findOne(array("_id" => $theObjId));

$connection->close();

?>
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