Thanks guys that was perfect
On Apr 14, 3:53 pm, Alex Gaynor <alex.gay...@gmail.com> wrote:
> On Tue, Apr 14, 2009 at 10:50 AM, veearrsix <stup...@googlemail.com> wrote:
>
> > Thanks for the help so far guys, I've used that recipe suggested by
> > Malcolm, where by I pass a number of querysets into the method. It
> > works as expected I guess, BUT, I would like to be able to sort by the
> > datetime field from each queryset, however the fieldnames for each of
> > the date time fields from each queryset are different. Is there a way
> > around this, should I actually be looking at a custom sql query?
>
> > On Apr 11, 12:55 am, Alex Gaynor <alex.gay...@gmail.com> wrote:
> > > On Fri, Apr 10, 2009 at 7:52 PM, Malcolm Tredinnick <
>
> > > malc...@pointy-stick.com> wrote:
>
> > > > On Fri, 2009-04-10 at 19:44 -0400, Alex Gaynor wrote:
>
> > > > > On Fri, Apr 10, 2009 at 7:40 PM, Malcolm Tredinnick
> > > > > <malc...@pointy-stick.com> wrote:
> > > > [...]
>
> > > > > Particularly with iterators, storing the (next head item,
> > rest
> > > > > of
> > > > > iterator) pair in a heap leads to a very neat and fast way to
> > > > > create a
> > > > > combined iterator. Here's one professional-quality
> > > > > implementation that I
> > > > > would recommend:http://code.activestate.com/recipes/491285/
>
> > > > > It has one unfortunate failing(which is the fault of the heapq
> > > > > library), it doesn't take a key/cmp function like sorted does. It is
> > > > > otherwise completely excellent though.
>
> > > > It's Python and so is the heap module! Modifying things is easy. I've
> > > > used the same solution with custom comparison functions one a number of
> > > > occasions. Even writing a small heap implementaiton with a custom
> > > > comparison is only about two dozen lines. Come on, think a little bit
> > > > outside the box!
>
> > > I'm not! A heap sort is a great solution to this problem(but you already
> > > knew that), it's just that the implementation in the python stdlib
> > doesn't
> > > work perfectly for this usecase(indeed I filed a ticket about this
> > upsteam
> > > several months ago, for reference it was rejected). I did the same thing
> > > you suggested for a blog post on this topic a number of months ago,
> > however
> > > it wasn't nearly as optimial as this(I believe you even commented to that
> > > effect on the post).
>
> > > > Regards,
> > > > Malcolm
>
> > > 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
>
> Well, if you use some sorting mechanism that takes a key function(like the
> one sorted takes) you could write one up that's something like:
>
> DATE_FIELD_MAPPING = {
> Model1: 'date',
> Model2: 'pubdate',
>
> }
>
> def my_key_func(obj):
> return getattr(obj, DATE_FIELD_MAPPING[type(obj)])
>
> And then sorted(chain(Model1.objects.all(), Model2.objects.all()),
> key=my_key_func)
>
> Or something similar using the heap sort method malcolm and I discussed.
>
> 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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