On Wed, 2012-02-08 at 09:53 -0500, Dennis Lee Bieber wrote:
> On Tue, 7 Feb 2012 21:23:58 -0800 (PST), akaariai <akaar...@gmail.com>
> wrote:
>
> >I think you could do
> >Customer.objects.annotate(tot_invoice=Sum(invoice_set__total_invoice)).order_by('tot_invoice')
> >[0:10].
>
> NOTE: the OP needs a /descending/ sort order (wants the 10 highest
> totals, not the 10 lowest).
>
> This may be an example of why I find SQL more understandable than
> the object-based approaches [caveat: I'm no where near familiar with
> Django's full query model], unless the back-end database feeds records
> from the result set on-demand... Transferring a large result set back to
> the client side just to slice off the first 10 entries just seems
> inefficient over having the DBMS itself limit the data set (I don't
> think the slice is "present" early enough to be turned into an "offset x
> limit y" query). Having to transfer the entire result set just to access
> the last 10 seems even more inefficient.
>
> --
> Wulfraed Dennis Lee Bieber AF6VN
> wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/
>
The only change you would need to make is to change the order_by clause
to .order_by('-tot_invoice'). This will not transfer the entire result
set. Django implements the slicing so that it is done at the sql
level.
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