Hi,
I noticed something strange with filtering related objects. Below is a
complete sample demonstrating the problem. This is only for demonstrating
the problem.
Django version is 1.9.1
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.
Am I missing something or does this seem like a bug?
Greets,
Balázs
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