On Sat, 2009-04-11 at 01:02 -0700, nikita kozlovsky wrote:
> On Apr 11, 3:11 am, Malcolm Tredinnick <malc...@pointy-stick.com>
> wrote:
>
>
> > Django's SQL is going exactly what you suspect and not using any outer
> > join here. Using a simplified version of the original two models:
> >
> > class Student(models.Model):
> > ...
> >
> > class Message(models.Model):
> > title = models.CharField(max_length=50)
> > student = models.ForeignKey(Student)
> >
> > ... the SQL that is generated for Message.objects.filter(student=None)
> > is:
> >
> > SELECT `outer_message`.`id`, `outer_message`.`title`,
> > `outer_message`.`student_id` FROM `outer_message` WHERE
> > `outer_message`.`student_id` IS NULL
>
> Yes, this correctly if student = models.ForeignKey(Student).
> I use this simplified models with student = models.ForeignKey
> (Student, null=True), sql that is generated for Message.objects.filter
> (student=None) is:
>
> SELECT "messages_message"."id", "messages_message"."title",
> "messages_message"."student_id" FROM "messages_message" LEFT OUTER
> JOIN "messages_student" ON ("messages_message"."student_id" =
> "messages_student"."id") WHERE "messages_student"."id" IS NULL
That's definitely a small bug, then. I've opened ticket #10790 so that
it gets fixed eventually. Since it's not a functionality bug (the answer
is still correct), it will be fixed after 1.1 now, but we will fix it. I
understand why it's occurring (the comparison to NULL is a very special
case in this situation).
Regards,
Malcolm
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