On Mon, Feb 22, 2010 at 4:48 AM, felix <crucialfe...@gmail.com> wrote:
>
> This seems so blatant that it couldn't really be a bug without someone
> noticing. Django 1.2
>
> qs = Apt.objects.filter(list_on_web=True,is_available=True)
>
> # FastAdderStatus has Apt and Service as fk
> qs = qs.filter(fastadderstatus__service=self.service)
>
> # later on here's another filter on the same table
> qs = qs.filter(fastadderstatus__running_status__in= (2, 3, 4))
>
> produces this:
>
> SELECT U0."id" FROM "nsproperties_apt" U0 INNER JOIN
> "fastadder_fastadderstatus" U1 ON (U0."id" = U1."apt_id") INNER JOIN
> "fastadder_fastadderstatus" U3 ON (U0."id" = U3."apt_id") WHERE
> (U0."list_on_web" = True AND U0."is_available" = True AND
> U1."service_id" = 4 AND U3."running_status" IN (2, 3, 4))
>
> Note that it joins the same table twice, and the Apt is not returning
> distinct. Postgres is not liking the query.
>
> count: 2837
>
> [<Apt: Property #12297>, <Apt: Property #12297>, <Apt: Property
> #12297>, <Apt: Property #12304>, <Apt: Property #12304>, <Apt:
> Property #12304>, <Apt: Property #12305>, <Apt: Property #12305>,
> <Apt: Property #12305>, <Apt: Property #12308>, <Apt: Property
> #12308>, <Apt: Property #12308>, <Apt: Property #12309>, <Apt:
> Property #12309>, <Apt: Property #12309>, <Apt: Property #12311>,
> <Apt: Property #12311>, <Apt: Property #12311>, <Apt: Property
> #12314>, <Apt: Property #12314>, '...(remaining elements
> truncated)...']
>
> what it should say (manually fixed) :
>
> SELECT U0."id" FROM "nsproperties_apt" U0 INNER JOIN
> "fastadder_fastadderstatus" U1 ON (U0."id" = U1."apt_id") WHERE
> (U0."list_on_web" = True AND U0."is_available" = True AND
> U1."service_id" = 4 AND U1."running_status" IN (2, 3, 4))
>
> count: 611, no dups
>
>
> My solution:
>
> params = {}
> if self.service:
> params['fastadderstatus__service'] = self.service
> if self.agent:
> params['agents'] = self.agent
>
> if self.status:
>
> params.update(
> FastAdderStatus.objects.filter_params_for_status(self.status,'fastadderstatus')
> )
>
> # a single call to filter
> qs = qs.filter(**params)
>
> which avoids the (?) bug and also is vastly more efficient.
You haven't found a bug - Django is returning exactly what you asked
for. There is a difference between making the query:
Model.objects.filter(a__b=x).filter(a__c=y)
and the query:
Model.objects.filter(a__b=x, a__c=y).
In the first query, Django will use two different joins on the 'A'
table. In the second query, the join on 'A' will be reused. It sounds
like what you want is the second query.
This behaviour is documented here [1].
[1]
http://docs.djangoproject.com/en/dev/topics/db/queries/#spanning-multi-valued-relationships
Yours,
Russ Magee %-)
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