Types

MongoDB allows programmers to save and query for data expressed in all of the basic PHP types, compound types (arrays, associative arrays, and objects), and a half-dozen classes provided by the MongoDB PHP driver (for regular expressions, dates, and other specialized applications).

Simple Types

The built-in types are:

Type	Description	Size in MongoDB (bytes)
NULL	Fairly self-explanatory.	0
boolean	TRUE and FALSE	1
int	Integer values.	4
float	Double values.	8
string	Strings of UTF-8 characters.	string length + 1

Arrays and Objects

Arrays and objects can also be saved to the database. An array with ascending numeric keys will be saved as a an array, anything else will be saved as an object.

<?php

// $scores will be saved as an array
$scores = array(98, 100, 73, 85);
$collection->insert(array("scores" => $scores));

// $scores will be saved as an object
$scores = array("quiz1" => 98, "midterm" => 100, "quiz2" => 73, "final" => 85);
$collection->insert(array("scores" => $scores));

?>

If you query for these objects using the database shell, they will look like:

> db.students.find()
{ "_id" : ObjectId("4b06beada9ad6390dab17c43"), "scores" : [ 98, 100, 73, 85 ] }
{ "_id" : ObjectId("4b06bebea9ad6390dab17c44"), "scores" : { "quiz1" : 98, "midterm" : 100, "quiz2" : 73, "final" : 85 } }

The database can also save arbitrary PHP objects (although they will be returned as associative arrays). The fields are used for the key/value pairs. For example, a blog post might look like:

<?php

  // the blog post class
  class Post {

  var $author;
  var $content;
  var $comments = array();
  var $date;

  public function __construct($author, $content) {
  $this->author = $author;
$this->content = $content;
    $this->date = new MongoDate();
  }

  public function setTitle($title) {
    $this->title = $title;
  }
}

// create a simple blog post and insert it into the database
$post1 = new Post("Adam", "This is a blog post");

$blog->insert($post1);


// there is nothing restricting the type of the "author" field, so we can make 
// it a nested object
$author = array("name" => "Fred", "karma" => 42);
$post2 = new Post($author, "This is another blog post.");

// we create an extra field by setting the title
$post2->setTitle("Second Post");

$blog->insert($post2);

?>

From the database shell, this will look something like:

> db.blog.find()
{ "_id" : ObjectId("4b06c263edb87a281e09dad8"), "author" : "Adam", "content" : "This is a blog post", "comments" : [ ], "date" : "Fri Nov 20 2009 11:22:59 GMT-0500 (EST)" }
{ "_id" : ObjectId("4b06c282edb87a281e09dad9"), "author" : { "name" : "Fred", "karma" : 42 }, "content" : "This is a blog post", "comments" : [ ], "date" : "Fri Nov 20 2009 11:23:30 GMT-0500 (EST)", "title" : "Second Post" }

The driver will not detect reference loops in arrays and objects. For example, this will give a fatal error:

<?php

$collection->insert($GLOBALS);

?>

Fatal error: Nesting level too deep - recursive dependency?

If you need to insert documents that may have recursive dependency, you have to check for it yourself before passing it to the driver.

MongoDB Types

The Mongo PHP driver also defines a few new types to use with the database. See class documentation for details and examples.

Type	Description	Size in MongoDB (bytes)
MongoBinData	Binary data.	Number of bytes in binary data + 5
MongoCode	JavaScript code.	String length of code + object size of scope.
MongoDate	Dates and times. Stored as milliseconds since the epoch.	8
MongoId	Unique document id: 4 bytes of timestamp No two records can have the same id if they were inserted at different times. 3 bytes machine id No two records can have the same id if they were inserted on different machines 2 bytes thread id No two records can have the same id if they were inserted by different threads running on the same machine. 3 bytes incrementing value Each time an id is created, a global counter is incremented and used as the increment value of the next id. Thus, no two records can have the same id unless a single process on a single machine managed to insert 256^3 (over 16 million) documents in one second, overflowing the increment field.	12
MongoMinKey	Always smaller than any other value.	String length of code + object size of scope.
MongoMaxKey	JavaScript code.	Always larger than any other value.
MongoRegex	Regular expressions.	Number of characters in regular expression + number of flags
MongoTimestamp	Replication timestamp	8

BSON

MongoDB uses a storage format called "BSON," Binary Serializable Object Notation, which is similar to JSON but more compact and rich in types. Listed below is the exact byte size of each type (or information required to compute its size, in the case of variable-length types). Keep in mind that these sizes do not include field names. The size of an object can be manually computed, but it may be easier for programmers to call the bson_encode() function and take the length of the resulting string.

An example of manually computing BSON size for saving the object array("x" => null, "y" => 40):

4 bytes (object size)

1 byte  (type of "x" field)
2 bytes ("x" and "\0")
0 bytes (for null)

1 byte  (type of "y" field)
2 bytes ("y" and "\0")
4 bytes (for an integer)

1 byte  (end-of-object byte)
-----------------------
15 bytes