Re: Can the new `Prefetch` solve my problem?

Thanks a lot for your answer :)

I will definitely use it from now on.

On 03/03/2015 06:59 AM, Simon Charette wrote:

Hi cool-RR,

The following should do:

filtered_chairs = Chair.objects.filter(some_other_lookup=whatever)
desks = Desk.objects.prefetch_related(
    PrefetchRelated('chairs', filtered_chairs, to_attr='filered_chairs'),
    PrefetchRelated('nearby_chairs', filtered_chairs, to_attr='filtered_nearby_chairs'),
)

from itertools import chain
for desk in desks:
    for chair in chain(desk.filtered_chairs, desk.filtered_nearby_chairs):
        # ....

It will issue only three queries independently of the number of Chair or Desks you have.

Simon

Le mercredi 25 février 2015 15:05:50 UTC-5, cool-RR a écrit :

Hi guys,

I'm trying to solve a problem using the new `Prefetch` but I can't figure out how to use it. 

I have these models:

    class Desk(django.db.models.Model):

        pass

    

    class Chair(django.db.models.Model):

        desk = django.db.models.Foreignkey('Desk', related_name='chair',)

        nearby_desks = django.db.models.ManyToManyField(

            'Desk',

            blank=True,

        )

I want to get a queryset for `Desk`, but it should also include a prefetched attribute `favorite_or_nearby_chairs`, whose value should be equal to: 

    Chair.objects.filter(

        (django.db.models.Q(nearby_desks=desk) | django.db.models.Q(desk=desk)),

        some_other_lookup=whatever,

    )

Is this possible with `Prefetch`? I couldn't figure out how to use the arguments.

Thanks,

Ram.

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