#10790: Too many joins in a comparison for NULL.
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Reporter: mtredinnick | Owner: mtredinnick
Status: new | Milestone:
Component: ORM aggregation | Version: SVN
Resolution: | Keywords:
Stage: Accepted | Has_patch: 0
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Changes (by wallenfe):
* cc: [email protected] (added)
Comment:
This becomes a more severe problem when it is combined with an update.
Due to the JOIN in the query, the update becomes two SQL statements rather
than one. This opens the door to potential race conditions if the web
server processes that are executing these statements end up interleaving
them.
To continue your example:
{{{
s=Student.objects.get(pk=1)
Message.objects.filter(student=None).update(student=s)
}}}
We get this:
{{{
SELECT `outer_message`.`id`, `outer_message`.`title`,
`outer_message`.`student_id`
FROM `outer_message`
LEFT OUTER JOIN `outer_student`
ON (`outer_message`.`student_id` = `outer_student`.`id`)
WHERE `outer_student`.`id` IS NULL
UPDATE `outer_message` SET `student_id` = 1 WHERE `outer_message`.`id` IN
(1)'
}}}
when ideally we should get:
{{{
UPDATE `outer_message` SET `student_id` = 1 WHERE
`outer_message`.`student_id` IS_NULL'
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/10790#comment:2>
Django <http://code.djangoproject.com/>
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