On Thu, 2009-09-24 at 06:25 -0700, blumenkraft wrote:
> Hi,
>
> It seems that Django generates too many joins with chained filters:
>
> class Issue(models.Model):
> is_opened = models.BooleanField()
>
> class Advertisement(models.Model):
> issues = models.ManyToManyField(Issue, null = True)
>
> >>> x = models.Advertisement.objects.filter(issues__is_opened =
> >>> True).filter(issues__is_opened = False)
> >>> print x._as_sql()
>
> ('SELECT U0.`id` FROM `publish_advertisement` U0 INNER JOIN
> `publish_advertisement_issues` U1 ON (U0.`id` = U1.`advertisement_id`)
> INNER JOIN `publish_issue` U2 ON (U1.`issue_id` = U2.`id`) INNER JOIN
> `publish_advertisement_issues` U3 ON (U0.`id` = U3.`advertisement_id`)
> INNER JOIN `publish_issue` U4 ON (U3.`issue_id` = U4.`id`) WHERE
> (U2.`is_opened` = %s AND U4.`is_opened` = %s )',
> (True, False))
>
> Is it expected behavior? If so how can I bypass it (still using
> chained filters)?
How is that too many? An advertisement can have many issues, you are
querying for advertisements that have an issue that is_opened and also
an issue that is not is_opened. If it did it with only one join to
`publish_issue`, it would not have the same meaning.
Cheers
Tom
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