#30246: Using an annotated field calculated with 
django.db.models.functions.Extract
in aggregate results in ProgrammingError
-------------------------------------+-------------------------------------
     Reporter:  Jan BaryƂa           |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  2.1
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:  query, aggregate,    |             Triage Stage:
  extract, annotate                  |  Unreviewed
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------

Comment (by Simon Charette):

 Hello Jan, thank you for your report.

 Just a few questions.

 You said the code worked fine on 1.8 but the `Aggregate(filter)` argument
 [https://docs.djangoproject.com/en/2.1/topics/db/aggregation/#filtering-
 on-annotations was only introduced in Django 2.0] and the `Extact`
 function [https://docs.djangoproject.com/en/1.10/ref/models/database-
 functions/ was only added in Django 1.10]. Were you using an explicit
 `Case(When(...))` in Django 1.8? Does using a `Case(When(...))` on Django
 2.1 happens to work around the issue? If not could you try to
 [https://docs.djangoproject.com/en/2.1/internals/contributing/triaging-
 tickets/#bisecting-a-regression bisect the change that broke it].

 You said you tried against 2.1 but did you try against the
 [https://pypi.org/project/Django/2.2b1/ current 2.2 beta as well]?

 Finally I think your misunderstood how to force the ORM to perform group
 by. I think what you are after is something along the lines of

 {{{#!python
 MyModel.objects.values('usage_time__hour').annotate(Sum('usage'))
 }}}

 And perform the hour labeling on the python side.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/30246#comment:1>
Django <https://code.djangoproject.com/>
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