#10417: Some model instances returned from a query set do not have any
attributes
filled in.
------------------------------------------+---------------------------------
Reporter: kevinvw | Owner: nobody
Status: new | Milestone: 1.1 beta
Component: Database layer (models, ORM) | Version: SVN
Keywords: Q, "multi-table inheritance" | Stage: Unreviewed
Has_patch: 0 |
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By combining two Q functions in my queryset with a OR (|) relation between
them over a multi-table inherited model, i get the following bug:
== Example of bug ==
{{{
>>> p = Project.objects.get(pk=1)
>>> for member in
StaffMember.objects.all().filter(Q(publications_as_author__belongsTo = p)
| Q(publications_as_coauthor__belongsTo = p)):
... print member.pk
...
3
4
>>> for member in
StaffMember.objects.all().filter(Q(publications_as_author__belongsTo = p)
| Q(publications_as_coauthor__belongsTo = p)):
... print member.first_name
...
Sven
None # << the bug, should be "Kevin". as proven on the line below.
>>> member = StaffMember.objects.get(pk=4)
>>> member.first_name
u'Kevin'
}}}
rozwell from #django had the following to say about this bug:
01:24 < rozwell> so it seems to me that this is happening when the
queryset gets collapsed into a list of model instances
== Necessary information to reproduce bug ==
{{{
class Publication(models.Model):
titled = models.CharField(max_length=255)
co_authors = models.ManyToManyField('StaffMember',
related_name="publications_as_coauthor")
belongsTo = models.ManyToManyField('Project',
related_name="has_publications")
authors = models.ManyToManyField('StaffMember',
related_name="publications_as_author")
admin.site.register(Publication)
class Project(models.Model):
named = models.CharField(max_length=255)
hasStaffMembers = models.ManyToManyField('StaffMember',
related_name="workson")
admin.site.register(Project)
class Person(models.Model):
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
# if you uncomment this line, you'll notice that the django shell throws
an exception
# because it can't concattenate None to String.
# first_name is apparently None in that instance (but it's not.)
# and last_name is apparently "" in that instance (but again, it's not, in
my case it was "Van Wilder".
# def __str__(self):
# return self.first_name + " " + self.last_name
admin.site.register(Person)
class StaffMember(Person):
works_at = models.CharField(max_length=255)
}}}
== SQL Query ==
The resulting SQL query from the queryset is as follows, but seemed okay:
{{{
>>> StaffMember.objects.all().filter(Q(publications_as_author__belongsTo =
p) | Q(publications_as_coauthor__belongsTo = p)).query.as_sql()
('SELECT "wsdmsite_person"."id", "wsdmsite_person"."first_name",
"wsdmsite_person"."last_name", "wsdmsite_staffmember"."person_ptr_id",
"wsdmsite_staffmember"."works_at" FROM "wsdmsite_staffmember" LEFT OUTER
JOIN "wsdmsite_publication_authors" ON
("wsdmsite_staffmember"."person_ptr_id" =
"wsdmsite_publication_authors"."staffmember_id") LEFT OUTER JOIN
"wsdmsite_publication" ON ("wsdmsite_publication_authors"."publication_id"
= "wsdmsite_publication"."id") LEFT OUTER JOIN
"wsdmsite_publication_belongsTo" ON ("wsdmsite_publication"."id" =
"wsdmsite_publication_belongsTo"."publication_id") LEFT OUTER JOIN
"wsdmsite_publication_co_authors" ON
("wsdmsite_staffmember"."person_ptr_id" =
"wsdmsite_publication_co_authors"."staffmember_id") LEFT OUTER JOIN
"wsdmsite_publication" T7 ON
("wsdmsite_publication_co_authors"."publication_id" = T7."id") LEFT OUTER
JOIN "wsdmsite_publication_belongsTo" T8 ON (T7."id" =
T8."publication_id") INNER JOIN "wsdmsite_person" ON
("wsdmsite_staffmember"."person_ptr_id" = "wsdmsite_person"."id") WHERE
("wsdmsite_publication_belongsTo"."project_id" = %s OR T8."project_id" =
%s )', (1, 1))
>>>
}}}
== Notes ==
If I remove any of the two Q functions and the OR relationship, it works
perfectly as you would expect it:
{{{
>>> p = Project.objects.get(pk=1)
>>> StaffMember.objects.all().filter(Q(publications_as_author__belongsTo =
p))
[<StaffMember: StaffMember object>]
>>> StaffMember.objects.all().filter(Q(publications_as_author__belongsTo =
p))[0].first_name
u'Kevin'
>>> StaffMember.objects.all().filter(Q(publications_as_coauthor__belongsTo
= p))
[<StaffMember: StaffMember object>]
>>> StaffMember.objects.all().filter(Q(publications_as_coauthor__belongsTo
= p))[0].first_name
u'Sven'
}}}
So i would guess it has something to do with the OR relationship.
--
Ticket URL: <http://code.djangoproject.com/ticket/10417>
Django <http://code.djangoproject.com/>
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