#25339: Aggregation and annotation by time period and intervals (by month, week,
day, hour, etc)
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Reporter: malefice | Owner: nobody
Type: New feature | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords: QuerySet.extra
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I often found that aggregation of data by dynamically generating time
periods given a desired time interval is a very sought after feature. I
personally created the snippet below to accommodate my needs, but as per
the note
[https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.extra
here], the extra() method will be deprecated soon. I think it will be a
waste to deprecate this API, since there is simply a lot of DBMS-specific
SQL functions available, but if there is any way we can do this via Django
ORM, then I am still up for it. The snippet below shows a custom QuerySet
method I often use.
{{{#!python
def get_metrics(self, frequency):
select_fields = OrderedDict()
if frequency == 'week':
select_fields['time_period'] = "date_trunc(%s,
initial_timestamp::TIMESTAMP WITH TIME ZONE AT TIME ZONE %s + '1
day'::interval) - '1 day'::interval"
else:
select_fields['time_period'] = "date_trunc(%s,
initial_timestamp::TIMESTAMP WITH TIME ZONE AT TIME ZONE %s)"
select_params = (frequency, settings.TIME_ZONE,)
queryset = self.extra(select=select_fields,
select_params=select_params).values('time_period', ....)
queryset = queryset.annotate(
# Add annotations
)
return queryset
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25339>
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