[Django] #25861: Performing two conditional counts on foreign key fields
Django
-------------------------------+----------------------------
Reporter: luccascorrea | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.8
Severity: Normal | Keywords: QuerySet.extra
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+----------------------------
I am just posting this because the documentation advises to file a ticket
whenever it is not possible to not use a queryset's "extra" method when
performing a query.
I was not able to perform the following query using only the ORM and not
relying on the "extra" method:
{{{
class Article(model.Model):
title = models.CharField(max_length=100, null=True)
body = models.TextField(null=True)
pubDate = models.DateTimeField()
class ArticleLike(models.Model):
article = models.ForeignKey('article.Article')
author = models.ForeignKey('accounts.User')
class ArticleView(models.Model):
article = models.ForeignKey('article.Article')
author = models.ForeignKey('accounts.User')
articles = Article.objects.extra(select={
"likesCount": "SELECT COUNT(DISTINCT `article_articlelike`.`id`) FROM
`article_articlelike` WHERE `article_articlelike`.`date` >=
`article_article`.`pubDate` AND `article_articlelike`.`article_id` =
`article_article`.`id`",
"viewsCount": "SELECT COUNT(DISTINCT `article_articleview`.`id`)
FROM `article_articleview` WHERE `article_articleview`.`date` >=
`article_article`.`pubDate` AND `article_articleview`.`article_id` =
`article_article`.`id`"
}}}
To make it clearer, the question this query is trying to answer is: how
many likes and views did each article receive after it was published?
It seems kind of odd that an article would be liked and viewed before
being published but the thing is that the article could be republished and
in this situation its pubDate would be updated, and so it should not take
into account the likes/views received before being republished, however
these likes/views cannot be deleted as to maintain a history of
likes/views.
So the problem is simple, two simultaneous conditional counts, where the
condition is in two foreign keys.
I was not able to use "annotate(likesCount=..., viewsCount=..)" because
the "count" ends up multiplying both annotations.
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Ticket URL: <https://code.djangoproject.com/ticket/25861>
Django <https://code.djangoproject.com/>
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Django
Reporter: luccascorrea | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.8
Keywords: QuerySet.extra | Triage Stage: Unreviewed
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by luccascorrea):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
--
Ticket URL: <https://code.djangoproject.com/ticket/25861#comment:1>
Django
Reporter: luccascorrea | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.8
Keywords: QuerySet.extra | Triage Stage: Unreviewed
Easy pickings: 0 | UI/UX: 0
Comment (by jarshwah):
Does this query work correctly?
{{{
from django.db.models import Count
from django.db.models.expressions import Case, When
likes = Q()
Article.objects.annotate(
likes=Count(
Case(When(articlelike__date__gte=F('pubdate'), then=1, else=0)),
distinct=True
),
views=Count(
Case(When(articleview__date__gte=F('pubdate'), then=1, else=0)),
distinct=True
)
)
}}}
I'm guessing this will result in duplicates also, but can you give it a
try anyway?
The ORM doesn't do aggregation across multiple reverse relations (or m2m
relations) very well. I'm not too certain about the reason unfortunately.
Anssi would know better than I, but I suspect it has something to do with
not creating subqueries.
--
Ticket URL: <https://code.djangoproject.com/ticket/25861#comment:2>
Django
Reporter: luccascorrea | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.8
Keywords: QuerySet.extra | Triage Stage: Unreviewed
Easy pickings: 0 | UI/UX: 0
Changes (by timgraham):
* Attachment "t25861.tar.gz" added.
Django
Reporter: luccascorrea | Owner: nobody
Type: Uncategorized | Status: closed
Component: Database layer | Version: 1.8
(models, ORM) | Resolution:
Severity: Normal | worksforme
Keywords: QuerySet.extra | Triage Stage:
| Unreviewed
Easy pickings: 0 | UI/UX: 0
Changes (by timgraham):
* status: new => closed
* resolution: => worksforme
* component: Uncategorized => Database layer (models, ORM)
Old description:
New description:
I am just posting this because the documentation advises to file a ticket
whenever it is not possible to not use a queryset's "extra" method when
performing a query.
I was not able to perform the following query using only the ORM and not
relying on the "extra" method:
{{{
class Article(models.Model):
--
Comment:
This query seems to work for me:
{{{
Article.objects.annotate(
likes=Count(
Case(When(articlelike__date__gte=F('pubDate'),
then=F('articlelike__id'))),
distinct=True
),
views=Count(
Case(When(articleview__date__gte=F('pubDate'),
then=F('articleview__id'))),
distinct=True
)
)
}}}
I've attached the sample project I used for testing.
--
Ticket URL: <https://code.djangoproject.com/ticket/25861#comment:3>