If I undestand the problem correctly, in MySQL you could do this in
one query as:
select
m.*,
(select min(created) from model2 where id = m.model2_id) as
first_created,
(select max(created) from model2 where id = m.model2_id) as
last_created
from model1 m
;
I don't know how that translates to the Django ORM (or even if it
does), though.
-Dave
On Dec 8, 12:27 am, Malcolm Tredinnick <[EMAIL PROTECTED]>
wrote:
> On Sat, 2008-12-06 at 20:56 -0800, erikcw wrote:
> > Hi all,
>
> > I'm trying to write a model query that will return a queryset along
> > with the latest (and earliest) data from 2 related models.
>
> > Right now I'm doing something like this:
>
> > objects = Model1.objects.filter(user=3).select_related() #about 6,000
> > objects
>
> > data = {}
> > for o in objects:
> > data[o.name] = [o.field1, o.field2]
> > data[o.name].append(o.field3.model2_set.all().latest('created'))
> > #get latest row from related model2
> > data[o.name].append(o.model3_set.all().order_by('created')[0])
> > #get earliest row from related model3
>
> > The problem is that this results in a TON of database queries. This
> > view is taking over a minute to process. The select_related on the
> > first line doesn't seem to be helping since I'm using latest()/
> > order_by which generates a new query.
>
> > How can I make this more efficient? Denormalizing the isn't an option
> > since model2 and model 3 are many-to-one.
>
> By the way (since I still haven't worked out the complex SQL to make it
> three queries yet), this last statement isn't correct. Denormalising
> doesn't just mean flattening. You can store a computed dependent field
> in model1 for the related information. So you could, for example, store
> the relevant date and pk value of the related model2 row and update that
> whenever a new model2 is inserted.
>
> Malcolm
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