James, you misunderstood me.
There isn't supposed to be a `favorite_or_nearby_chairs`
attribute. That's the new attribute I want the prefetching to add
to the `Desk` queryset that I need. Also, I don't understand why
you'd tell me to add a `.select_related('nearby_desks')` to my
query. Are you talking about the query that starts with
`Chair.objects`? I'm not looking to get a `Chair` queryset. I'm
looking to get a `Desk` queryset, which has a prefetched
attribute `favorite_or_nearby_chairs` which contains the `Chair`
queryset I wrote down.
Thanks,
Ram.
On Thursday, February 26, 2015 at 6:02:15 AM UTC+2, James
Schneider wrote:
Well, the Desk model you provided is blank, but I'll believe
you that there's a favorite_or_nearby_chairs attribute. ;-)
Should be relatively simple. Just add a
.select_related('nearby_desks') to your existing query and
that should pull in the associated Desk object in a single
query. You can also substitute in prefetch_related(),
although you'll still have two queries at that point.
If you are trying to profile your site, I would recommend the
Django-debug-toolbar. That should tell you whether or not
that query set is the culprit.
-James
On Feb 25, 2015 1:28 PM, "Ram Rachum" <[email protected]> wrote:
Hi James,
I've read the docs but I still couldn't figure it out. My
queryset works great in production, I'm trying to
optimize it because our pageloads are too slow. I know
how to use querysets in Django pretty well, I just don't
know how to use `Prefetch`.
Can you give me the solution for the simplified example I
gave? This might help me figure out what I'm not
understanding. One thing that might be unclear with the
example I gave, is that I meant I want to get a queryset
for `Desk` where every desk has an attribute names
`favorite_or_nearby_chairs` which contains the queryset
of chairs that I desrcibed, prefetched.
Thanks,
Ram.
On Wed, Feb 25, 2015 at 11:18 PM, James Schneider
<[email protected]> wrote:
I assume that you are talking about the
select_related() and prefetch_related() queryset methods?
https://docs.djangoproject.com/en/1.7/ref/models/querysets/#select-related
https://docs.djangoproject.com/en/1.7/ref/models/querysets/#prefetch-related
Both of those sections have excellent examples, and
detail what the differences are (primarily joins vs.
separate queries, respectively).
For better help, you'll need to go into more detail
about the queries you are trying to make, what you've
tried (with code examples if possible), and the
results/errors you are seeing.
In general, I would try to get an initial queryset
working and gathering the correct results first
before looking at optimizations such as
select_related(). Any sort of pre-fetching will only
confuse the situation if the base queryset is incorrect.
-James
On Wed, Feb 25, 2015 at 12:05 PM, cool-RR
<[email protected]> wrote:
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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