I have a model which has a ForeignKey to itself, intended to mark
duplicates similar to a bug/ticket-tracking system:
class Bug(models.Model):
name = models.CharField(maxlength=64)
duplicate_of = models.ForeignKey('self', related_name='duplicates',
null=True)
def __str__(self):
return self.name
When searching through bug names for a particular string, I don't want
the duplicate bugs to appear; instead, I want both bugs with a matching
name and bugs whose set of duplicates contains one with a matching name.
I would have expected this filter to work:
Bug.objects.filter(
Q(name__contains=string) | Q(duplicates__name__contains=string),
duplicate_of__isnull=True)
It doesn't. Instead, I get this very surprising behavior:
>>> for t in Bug.objects.all():
... print t.name, t.duplicate_of
...
eggs1 None
eggs2 spam
spam None
>>> qs = Bug.objects.filter(duplicate_of__isnull=True)
>>> r1 = qs.filter(name__contains='eggs')
>>> r2 = qs.filter(duplicates__name__contains='eggs')
>>> r1
[<Bug: eggs1>]
>>> r2
[<Bug: spam>]
>>> r1 | r2
[<Bug: spam>]
>>>
It seems that this is because Django is using INNER JOIN in its query:
SELECT
"test_bug"."id","test_bug"."name","test_bug"."duplicate_of_id"
FROM
"test_bug"
INNER JOIN
"test_bug" AS "test_bug__duplicates"
ON
"test_bug"."id" = "test_bug__duplicates"."duplicate_of_id"
WHERE
(("test_bug"."duplicate_of_id" IS NULL AND
"test_bug"."name" LIKE %eggs% ESCAPE '\')
OR
("test_bug"."duplicate_of_id" IS NULL AND
"test_bug__duplicates"."name" LIKE %eggs% ESCAPE '\'))
Replacing the INNER JOIN with a LEFT OUTER JOIN gives me the results I
expected.
Is this a bug, or am I doing something silly?
-Zak
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