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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