mongodb - php - aggregate projection and match - php

Question

I'm trying to match criteria (cl=1) and then aggregate all the results by month (I've tried year/month/date as well to no luck).
When I run the code below it seems like it works properly, the output shows the months etc, however none of the stats are being added.
The $du field in Mongo is a MongoDate object.
Does anyone have any idea what I'm doing wrong?
See very bottom for a code snippet that is searched by date and returns a result.
$result = $collection->aggregate(
array(
array('$match' => array(
'cl' => $app_id) # application id, int such as "2"
),
array('$project' => array(
//'year' => array('$year' => '$du'),
'month' => array('$month' => '$du'),
//'week' => array('$week' => '$du'),
)),
array('$group' =>
array(
'_id' => array(
'month' => '$month',
),
'i' => array('$sum' => '$vs.i'),
'r' => array('$sum' => '$vs.r'),
'u' => array('$sum' => '$vs.u'),
)
),
array(
'$sort' => array(
'_id' => -1
)
),
array(
'$limit' => 14
)
)
);
Output:
Array
(
[result] => Array
(
[0] => Array
(
[_id] => Array
(
[month] => 10
)
[i] => 0
[r] => 0
[u] => 0
)
[1] => Array
(
[_id] => Array
(
[month] => 9
)
[i] => 0
[r] => 0
[u] => 0
)
.......
working - searching by date
$start = new MongoDate(strtotime("2012-10-01 00:00:00"));
$end = new MongoDate(strtotime("2013-10-15 00:00:00"));
$cursor = $collection->find(array("du" => array('$gt' => $start, '$lte' => $end)));
while ($cursor->hasNext()) {
$document = $cursor->getNext();
print_r($document);exit;
}
# RESPONSE
Array
(
[_id] => MongoId Object
(
[$id] => 51acbfd33dd49497848a8e5b
)
[cl] => 1
[du] => MongoDate Object
(
[sec] => 1370275795
[usec] => 0
)
[vs] => Array
(
[i] => 11
[u] => 1
)
)

Answer 1

The stats aren't there because you haven't chosen to project them. Project gives you _id by default, but anything else you want must be specified.
You'll need something like this instead of your current $project:
array('$project' => array(
'month' => array('$month' => '$du'),
'vs' => 1
))