Re: Django foreing keys joins

Thanks!,

that query is making the join, and i wan't tho make a faster query, Joins ar not slow but if i can avoid it better.

>>> print Counter.on_medicos.filter(loc_id__isnull=True).only('id').query

My solution was: instead of  put null values on empty relations, put a 0 value.. It work's very good.

Thank for your answer, 

p.s: Can you give me your opinion about that  question https://groups.google.com/forum/?fromgroups#!searchin/django-users/prefetch_related$20and$20only/django-users/im9LGioyWu8/8DrEnakoQKgJ?

2013/6/6 Jani Tiainen <redetin@gmail.com>

That is how Django works.

So as you see, django makes query where it compares _joined_ table id as a null. To make it happen (left outer) join must happen, otherwise it wouldn't return any rows.

I agree that Django _could_ do a better and optimize query so that it would query instead of underlying fk field as a null value, though that would not be simple since a you know, filters may be chained and in case of chaining rewriting whole query would require quite a bit of reworkings.

If you absolutely know that your query stops there you can use underlying id field for faster testing:

>>> print Counter.on_medicos.filter(loc_id__isnull=True).only('id').query

That should return what you might have been expecting.

--

Jani Tiainen

"Impossible just takes a little longer"

On Thu, 6 Jun 2013 01:05:32 +0200
Àlex Pérez <alex.perez@bebabum.com> wrote:

> Can someone tell me why the or in that query:
> print Counter.on_medicos.filter(loc__isnull=True).only("id").query
>
> ""SELECT `web_counter`.`id` FROM `web_counter` LEFT OUTER JOIN
> `locations_localidad` ON (`web_counter`.`loc` = `locations_localidad`.`id`)
> WHERE (`web_counter`.`mode` = 1  AND `locations_localidad`.`id` IS NULL)"""
>
> The orm is making a JOIN?? i can't understant!
>
> The foreignkey loc is nullable and blank, i don't understant why making a
> filter the orm is performing the join and making an exclude the ORM is not
> performing the JOIN...
>
> print Counter.on_medicos.exclude(loc__isnull=True).only("id").query
> SELECT `web_counter`.`id` FROM `web_counter` WHERE (`web_counter`.`mode` =
> 1  AND NOT (`web_counter`.`loc` IS NULL))
>
> Thank's!
>
> --
> Alex Perez
> alex.perez@bebabum.com
>

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--
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alex.perez@bebabum.com
 
 bebabum be successful

c/ Còrsega 301-303, Àtic 2
08008 Barcelona
http://www.bebabum.com
http://www.facebook.com/bebabum
http://twitter.com/bebabum

This message is intended exclusively for its addressee and may contain
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Este mensaje se dirige exclusivamente a su destinatario y puede contener
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queda notificado que la utilización, divulgación y/o copia sin autorización 
está prohibida en virtud de la legislación vigente.

Le informamos que los datos personales que facilite/ha facilitado pasarán a
formar parte de un fichero responsabilidad de bebabum, S.L. y que tiene 
por finalidad gestionar las relaciones con usted. 
Tiene derecho al acceso, rectificación cancelación y oposición en nuestra
oficina ubicada en c/ Còrsega 301-303, Àtic 2 de Barcelona o a la dirección de e-mail lopd@bebabum.com

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