sum by hours/days/month based on timestamp in mongoengine/pymongo - python-3.x

Question

At first - I am a beginner with mongodb. So i have next probleb. I am using such a model as below with mongoengine:
class Stats(Document):
Name = StringField(max_length=250)
timestamp = LongField(default=mktime(datetime.now().timetuple()))
count = IntField()
<some other fields>
What exactly I want is to filter by the name (it's clear) and use aggregation operation sum over field count. But I want to count the sum of records grouped by hours/days/months.
As example, if we have records with such timestamps [1532970603, 1532972103, 153293600, 1532974500], then 1-2 form first group, and 3-4 form second group.
And that is where I have stuck. I have some ideas about grouping by every n records, or by dividing timestamp on 3600
(1 hour = 3600 seconds), but how to make it with mongoengine. Or even how to insert some expressions with python in a pipeline?
I will very appreciate any help.

Answer 1

I would recommend to use ISO date format and store complete date in timestamp. Here is your model
class Stats(Document):
Name = Document.StringField(max_length=250)
timestamp = Document.DateTime(default=datetime.utcnow()) //ISO time format recommended
count = Document.FloatField()
meta = {'strict': False}
Now you can aggregate them accordingly.
Stats.objects.aggregate(
{
'$group': {
'_id': {'year': {$year: '$timestamp'},
'month': {$month: '$timestamp'},
'day' : {$dayOfMonth: '$timestamp'},
'hour': {'$hour: '$timestamp'},
}
}
}
)