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

On Tue, Mar 3, 2015 at 5:59 AM, Simon Charette <charette.s@gmail.com> 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

Does filtered_chairs get executed 'as-is', or is it then filtered by
the query to which it is attached? IE:

filtered_chairs = Chair.objects.filter(some_other_lookup=whatever)
desks = Desk.objects.filter(pk__range=(1,1000)).prefetch_related(
PrefetchRelated('chairs', filtered_chairs, to_attr='filered_chairs'),
PrefetchRelated('nearby_chairs', filtered_chairs,
to_attr='filtered_nearby_chairs'),
)

is filtered_chairs filtered by the 'desk__pk__range'?

Cheers

Tom

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