On Tue, Mar 3, 2009 at 11:32 AM, Ross <real...@gmail.com> wrote:
>
> Do you know a good way to do what I am trying to do? I can write a
> quick for loop to do the work, but I was hoping to offload some of the
> work to the database since it is much faster than a Python for loop.
>
> I have a set of say 10,000 Product models. I want to get a list of the
> 100 with the highest prices, which I currently do with this query:
>
> Product.objects.order_by("-price")[:100]
>
> I then want to know the maximum and minimum prices within that list. I
> was hoping I could use aggregation and let the database find the
> maximum and minimum for me, but that doesn't work as Alex said.
>
> On Mar 3, 10:08 am, Alex Gaynor <alex.gay...@gmail.com> wrote:
> > On Tue, Mar 3, 2009 at 8:55 AM, Ross <real...@gmail.com> wrote:
> >
> > > I have started using aggregation, but it seems to ignore any slicing I
> > > do on a QuerySet before calling aggregate. This is what I'm doing:
> >
> > > Product.objects.order_by("-price")[:100].values("price").aggregate(Max
> > > ("price"), Min("price"))
> >
> > > I want the maximum and minimum price for the products with the top 100
> > > largest prices. The aggregate function, however, returns the maximum
> > > and minimum price for all Products--it ignores the [:100] slice.
> >
> > > Is this an improper use of aggregation, or am I doing something wrong
> > > with my query?
> >
> > Before an aggregation is preformed all limits are removed, so you are
> seeing
> > expected behavior. I can't remember why this behavior exists though :/
> >
> > Alex
> >
> > --
> > "I disapprove of what you say, but I will defend to the death your right
> to
> > say it." --Voltaire
> > "The people's good is the highest law."--Cicero
> >
> You can always do:
prices = Produuct.objects.order_by('-price').values_list('price', flat=True)
min_price, max_price = min(prices), max(prices)
I'm assuming the limitation isn't arbitrary and the reason it isn't allowed
in the ORM is that it doesn't always work.
Alex
--
"I disapprove of what you say, but I will defend to the death your right to
say it." --Voltaire
"The people's good is the highest law."--Cicero
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