On Tue, 2007-05-29 at 06:56 +0000, Michael Newman wrote:
> Thanks for the reply and sorry for my vagueness;
>
> Rob: I was talking about really long lines of python. Thanks for the
> heads up about the all. I was just typing off the top of my head and
> still and figuring out python.
>
> Malcom: I suppose that is what I am asking. Is there any simple way
> to take group of objects like breakingnews in my example and exclude
> those objects from another set of objects (news) without a for
> statement?
No. The reasoning runs something like this: If you want to do something
in two queries like that, it's going to be because you want to filter
the intermediate results somehow. If you just want to extract the list
of ids that a straightforward list comprehension over the original
queryset, so it's not something we need to add extra support for.
If you care about getting every last bit of efficiency out of your
queries, you won't be doing two queries anyway (we cannot possibly get
information from the first queryset without running the query, since the
language is called Python, not Psychic), so this construct isn't
relevant there. There is a variation on this problem where you might
need to build nested queries or some such, but there's no support for
that at the moment. One day, maybe, but not today.
The "long lines" argument isn't really a problem, by the way. You can
happily write
qs = Story.objects.exclude(....)
qs = qs.filter(....)
qs = qs.count()
and no database queries will result. Querysets are only evaluated when
you access the results, not when you add constraints to them. So each
line need only contain one filter, if that's the way you wish to go.
Regards,
Malcolm
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