mongodb date aggregation operators timezone adjustments with php - php

Question

I'm trying to adjust the timezone with date aggregation operators.
I need to make -7 hours adjustment on the $signs.timestamp field.
This is my code:
function statsSignatures() {
$cursor = $this->db->collection->users->aggregate(
array('$unwind' => '$signs'),
array('$project'=>array(
'signs'=>'$signs',
'y'=>array('$year'=>'$signs.timestamp'),
'm'=>array('$month'=>'$signs.timestamp'),
'd'=>array('$dayOfMonth'=>'$signs.timestamp'),
'h'=>array('$hour'=>'$signs.timestamp')
)),
array('$group'=>array(
'_id'=>array('year'=>'$y','month'=>'$m','day'=>'$d','hour'=>'$h'),
'total'=>array('$sum'=>1)
)),
array('$sort'=>array(
'_id.year'=>1,
'_id.month'=>1,
'_id.day'=>1,
'_id.hour'=>1
))
);
return $cursor['result'];
}
I'm using MongoDB version 2.6.3.
Thank you a lot !

Answer 1

You can use $project with $subtract operator to make a -7 hour adjustment to a Date field:
{
$project : {
ts : { $subtract : [ "$signs.timestamp", 25200000 ] }
}
}
// 25200000 == 1000 milis x 60 sec x 60 mins x 7 h
The projected field ts is a Date that's offset by -7 hours.
Edit
This is the correct PHP syntax when using $subtract.
array(
'$project' => array(
'ts' => array('$subtract' => array('$signs.timestamp', 25200000))
)
)
Subtract accepts an array of values, not a key=>value pair.

Answer 2

I'm not sure why, but I'm getting "exception: invalid operator '$signs.timestamp'" if i'm trying to subtract this in php like this code:
$cursor = $app['mdb']->changemi->users->aggregate(
array('$unwind' => '$signs'),
array('$project' => array(
'ts'=>array('$subtract'=>array(
'$signs.timestamp'=> 25200000
))
)),
array('$project'=>array(
'y'=>array('$year'=>'$ts'),
'm'=>array('$month'=>'$ts'),
'd'=>array('$dayOfMonth'=>'$ts'),
'h'=>array('$hour'=>'$ts')
)),
array('$group'=>array(
'_id'=>array('year'=>'$y','month'=>'$m','day'=>'$d','hour'=>'$h'),
'total'=>array('$sum'=>1)
)),
array('$sort'=>array(
'_id.year'=>1,
'_id.month'=>1,
'_id.day'=>1,
'_id.hour'=>1
))
);
So I came with 2 workarounds:
backend php. json_decode
$cursor = $app['mdb']->changemi->users->aggregate(
array('$unwind' => '$signs'),
json_decode('{"$project" : {"ts" : { "$subtract" : [ "$signs.timestamp", 25200000 ] }}}',true),
array('$project'=>array(
'y'=>array('$year'=>'$ts'),
'm'=>array('$month'=>'$ts'),
'd'=>array('$dayOfMonth'=>'$ts'),
'h'=>array('$hour'=>'$ts')
)),
array('$group'=>array(
'_id'=>array('year'=>'$y','month'=>'$m','day'=>'$d','hour'=>'$h'),
'total'=>array('$sum'=>1)
)),
array('$sort'=>array(
'_id.year'=>1,
'_id.month'=>1,
'_id.day'=>1,
'_id.hour'=>1
))
);
frontend javascript (minusHours)
Date.prototype.minusHours= function(h){
this.setHours(this.getHours()-h);
return this;
}
...
"date": new Date({{ i._id.year }}, {{ i._id.month -1 }}, {{ i._id.day }}, {{ i._id.hour }}, 0, 0, 0).minusHours(7),

Answer 3

Here is what worked for me. Instead of doing the timezone conversion in the 'project', I just convert the timestamp while grouping.
group._id = {
year: { $year : [{ $subtract: [ "$timestamp", 25200000 ]}] },
month: { $month : [{ $subtract: [ "$timestamp", 25200000 ]}] },
day: { $dayOfMonth : [{ $subtract: [ "$timestamp", 25200000 ]}] }
};
group.count = {
$sum : 1
};

Answer 4

There's no need to close some objects in array, this way worked for me:
group._id = {
year: { $year : { $subtract: [ "$timestamp", 25200000 ]}},
month: { $month : { $subtract: [ "$timestamp", 25200000 ]}},
day: { $dayOfMonth : { $subtract: [ "$timestamp", 25200000 ]}}
};
group.count = {
$sum : 1
};