Re: Is this behavior with Meta Ordering and Group By expected?

Thanks!  I don't see how the link you provided justifies your point.  I don't see anything in there saying that specifying an ordering will subsume group by statements.  How did you know this was expected?

But..in any case I'm happy to take your word for it.  And thanks a bunch for the workaround!

-Eric

On Wednesday, June 29, 2016 at 3:12:08 PM UTC-7, Fabio Caritas Barrionuevo da Luz wrote:

Hi Eric. 

This is the expected behavior ( https://docs.djangoproject.com/en/dev/ref/models/options/#ordering ). 

If ordering is defined on model Meta, the ORDER BY SQL is included by default in all query.

to avoid this behavior, you can use order_by() without parameters: 

eg: 

A.objects.order_by().values('b').annotate(most_recent=Max('created_at'))

On Wed, Jun 29, 2016 at 5:39 PM, eric conner <ericw...@gmail.com> wrote:

Hello!

I'm using Django 1.9.7, MySQL innodb 5.7.11, and python 2.7.10.

I noticed some strange behavior when running this query:

q = A.objects.values('b').annotate(most_recent=Max('created_at'))

Produces this SQL:

SELECT `core_a`.`b_id`, MAX(`core_a`.`created_at`) AS `most_recent` FROM `core_a` GROUP BY `core_a`.`id` ORDER BY `core_a`.`id` ASC

which groups by an unexpected field.  I was expecting it to group by `core_a`.`b_id` rather than `core_a`.`id`.

Here are my models:

from __future__ import unicode_literals

from django.db import models

from django.utils import timezone

class B(models.Model):

    created_at = models.DateTimeField(default=timezone.now)

class A(models.Model):

    created_at = models.DateTimeField(default=timezone.now)

    b = models.ForeignKey(B)

    class Meta:

        ordering = ["id"]

If I remove from model A these lines 

    class Meta:

        ordering = ["id"]

then the query produces SQL which groups by the b_id column as expected.

Is this known behavior?  Would this be considered a bug?

Thanks,

-Eric

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Fábio C. Barrionuevo da Luz
Palmas - Tocantins - Brasil - América do Sul

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