Question

Take inner array of mongo document using with limit and skip in php.

$db->users->findOne(array('_id' => new MongoId('5045fa0213cfcdfc06000008')));

Above query will give me below mongo array

[_id] => MongoId Object (
    [$id] => 5045fa0213cfcdfc06000008
)
[items] => Array (
    [0] => 13
    [1] => 4
    [2] => 3
    [3] => 7
    [4] => 10
    [5] => 11
    [6] => 28
    [7] => 54
    [8] => 31
    [9] => 33
    [10] => 37
    [11] => 12
)

Is it possible to make use of limit with skip with above mongo doc, something like below

$db->users->
  findOne(array('_id' => new MongoId('5045fa0213cfcdfc06000008')))->
    limit(5)->skip(5);

Which will output as

[_id] => MongoId Object (
    [$id] => 5045fa0213cfcdfc06000008
)
[items] => Array (
    [5] => 11
    [6] => 28
    [7] => 54
    [8] => 31
    [9] => 33
)

And how to take total count of items array using mongo?

Answer 1

The limit() and skip() methods only apply at the document level, not the array level.

You can use the $slice operator to fetch a subset of an array:

$skip = 5;
$limit = 5;

$filter = array('_id' => new MongoId('5045fa0213cfcdfc06000008'));
$slice = array('items' => array( '$slice' => array( $skip, $limit ) ));

$db->users->findOne($filter, $slice);

There currently (as at MongoDB 2.2.0) isn’t a straightforward way to determine the size of the array without fetching it. You could do some manipulation using the new Aggregation Framework but that’s perhaps overkill.

A common usage pattern is to use $inc to adjust a counter in a document in the same update when items are added or removed from an array.

And how to take total count of items array using mongo?

Here is a quick example using the Aggregation Framework in the mongo shell:

db.users.aggregate(
    { $unwind: '$items' },
    { $group: {
        '_id': '$_id',
        itemcount: { $sum: 1 }
    }}
)