On Fri, 2009-04-10 at 16:44 -0400, Alex Gaynor wrote: > > > On Fri, Apr 10, 2009 at 4:40 PM, veearrsix <stup...@googlemail.com> > wrote: > > This question seems to have been asked a few times, but never > answered > fully.
Not quite true. It's been answered fully a lot of times: querysets are iterators, so you have multiple sorted iterators and combining them into a single sorted iterator is just a merge sort. Creating a single queryset is almost always not the real problem people are trying to solve. Which is fortunate, since it doesn't make sense on a definitional level: a queryset is the result of filtering a set of model results, not combining arbitrary SQL. Combining multiple querysets into a single result that can be iterated through is the typical problem trying to be solved. [...] > > There is no way to get a single QuerySet with results from multiple > models. What you want to do is best approximated like this: > > from itertools import chain > > sorted(chain(Model1.obejcts.all(), Model2.objects.all()), key=lambda > o: o.pub_date) That's a bit crufty, since it pulls everything into memory immediately. Not cool with a few tens of thousands items in the result set (creating all those Python objects is noticeable). Merge or heap sort is your friend here. Sure, us old guys have the advantage here, because that stuff was very standard back in the age of dinosaurs when RAM was scarcer and hard- and tape-drives were slower, so random access wasn't always an option. 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/ Regards, Malcolm --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
