Django queryset group by and count distincts

Question

In my django application, I have a set of donation, which I want to make statistics on. For each donation, a person is linked with his email address.

I want to compute for each month, the number of donors, that is the number of unique email addess.

So far I have:

# filter all donations by month
truncate_date = connection.ops.date_trunc_sql('month', 'date')
qs = Donation.objects.extra({'month': truncate_date})

# group by months and annotate each with the count of emails
donors = qs.values('month').annotate(count=Count('email')).order_by('month')

This works well, I get a monthly report of all email donors, but as I got duplicate in email, it does not filter email by unique values.

The current database used is Postgresql.

How this can be done?

Are you using postgres?

Sayse
– Sayse

2016-05-12 09:13:57 +00:00
Commented May 12, 2016 at 9:13 — Sayse
– Sayse, Commented May 12, 2016 at 9:13
Yes, I'll add this in the question.

nobe4
– nobe4

2016-05-12 09:14:26 +00:00
Commented May 12, 2016 at 9:14 — nobe4
– nobe4, Commented May 12, 2016 at 9:14

solarissmoke · Accepted Answer · 2016-05-12 09:14:57Z

7

Count takes a distinct argument, so you can do:

donors = qs.values('month').annotate(count=Count('email', distinct=True)).order_by('month')

answered May 12, 2016 at 9:14

solarissmoke

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