#26379: Inconsistent behaviour of filter() on related model (RelatedManager)
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Reporter: ignus2 | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Given the model in a "testapp" app:
{{{
############################
from django.db import models
class Blog(models.Model):
title = models.CharField(max_length=100)
# subscribers - related from Person
# subscriptions - related from Subscription
def __str__(self):
return self.title
class Person(models.Model):
name = models.CharField(max_length=100)
subscribed_blogs = models.ManyToManyField(Blog,
related_name="subscribers", through="Subscription")
# subscriptions - related from Subscription
def __str__(self):
return self.name
class Subscription(models.Model):
person = models.ForeignKey(Person, related_name="subscriptions")
blog = models.ForeignKey(Blog, related_name="subscriptions")
subscribed_date = models.DateField()
def __str__(self):
return ''.join([self.person.name, " - ", self.blog.title])
############################
}}}
When I filter "subscribers" of a Blog instance, the results are not
consistent.
Here is the code demonstrating the effect:
{{{
############################
from testapp.models import *
from datetime import datetime
adam = Person.objects.create(name="Adam")
blog_1 = Blog.objects.create(title="Blog 1")
blog_2 = Blog.objects.create(title="Blog 2")
Subscription.objects.create(person=adam, blog=blog_1,
subscribed_date=datetime(2016,1,10))
Subscription.objects.create(person=adam, blog=blog_2,
subscribed_date=datetime(2016,1,20))
queryparams = {"subscriptions__subscribed_date__gt": datetime(2016,1,15)}
q1 = blog_1.subscribers.filter(**queryparams)
q2 = blog_1.subscribers.all().filter(**queryparams)
q3 = blog_1.subscribers.get_queryset().filter(**queryparams)
print(q1.query)
print(q1)
print(q2.query)
print(q2)
print(q3.query)
print(q3)
print("--------------------------")
q1 = blog_1.subscribers.filter().filter(**queryparams)
q2 = blog_1.subscribers.all().all().filter(**queryparams)
q3 = blog_1.subscribers.get_queryset().all().filter(**queryparams)
print(q1.query)
print(q1)
print(q2.query)
print(q2)
print(q3.query)
print(q3)
############################
}}}
The output is:
{{{
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") WHERE
("testapp_subscription"."blog_id" = 1 AND
"testapp_subscription"."subscribed_date" > 2016-01-15)
[]
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") WHERE
("testapp_subscription"."blog_id" = 1 AND
"testapp_subscription"."subscribed_date" > 2016-01-15)
[]
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") WHERE
("testapp_subscription"."blog_id" = 1 AND
"testapp_subscription"."subscribed_date" > 2016-01-15)
[]
--------------------------
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") INNER JOIN
"testapp_subscription" T4 ON ("testapp_person"."id" = T4."person_id")
WHERE ("testapp_subscription"."blog_id" = 1 AND T4."subscribed_date" >
2016-01-15)
[<Person: Adam>]
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") INNER JOIN
"testapp_subscription" T4 ON ("testapp_person"."id" = T4."person_id")
WHERE ("testapp_subscription"."blog_id" = 1 AND T4."subscribed_date" >
2016-01-15)
[<Person: Adam>]
SELECT "testapp_person"."id", "testapp_person"."name" FROM
"testapp_person" INNER JOIN "testapp_subscription" ON
("testapp_person"."id" = "testapp_subscription"."person_id") INNER JOIN
"testapp_subscription" T4 ON ("testapp_person"."id" = T4."person_id")
WHERE ("testapp_subscription"."blog_id" = 1 AND T4."subscribed_date" >
2016-01-15)
[<Person: Adam>]
}}}
The first set of queries simply "AND" the filter params with the
"subscribers" RelatedManager's inherent related-filtering, while the
second set of queries do a separate chain filtering.
This is exactly the kind of situation that is described in the django docs
(with the blogs, "Lennon" and "2008"):
https://docs.djangoproject.com/en/dev/topics/db/queries/#spanning-multi-
valued-relationships
I believe the second set of queries should be the correct one, and that
should be happening also in the first set of queries, but that is not what
is happening.
--
Ticket URL: <https://code.djangoproject.com/ticket/26379>
Django <https://code.djangoproject.com/>
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