log_write_batch
Querying
Manual
PHP Manual

# Writes

## Updating Nested Objects

Suppose we wish to change the name of a comment's author in this document:

    {
        "_id" : ObjectId("4b06c282edb87a281e09dad9"),
        "content" : "this is a blog post.",
        "comments" :
        [
            {
                "author" : "Mike",
                "comment" : "I think that blah blah blah...",
            },
            {
                "author" : "John",
                "comment" : "I disagree."
            }
        ]
    }

In order to change an inner field, we use $set (so that all of the other fields are not removed!) with the index of comment to change:
`<?php
$blog->update($criteria, array('$set' => array("comments.1" => array("author" => "Jim"))));
?>`

## The Positional Operator

The positional operator $ is useful for updating objects that are in arrays. In the example above, for instance, suppose that we did not know the index of the comment that we needed to change, merely that we needed to change "John" to "Jim". We can use $ to do so.

`<?php
$blog->update(
array('comments.author' => 'John'),
array('$set' => array('comments.$.author' => 'Jim')));
?>`

log_write_batch
Querying
Manual
PHP Manual