On Sun, Aug 16, 2009 at 8:42 AM, David<davidsh...@googlemail.com> wrote: > > Hi all, > > I'm a bit puzzled by the caching behaviour of QuerySets, when used in > iteration and when called with repr(). According to the documentation, > when a QuerySet is evaluated for the first time, the results are > cached. > > Trying this out in the shell, this works as expected for iteration. > However when used with repr(), the QuerySet does not seem to be using > the cache, and I was just wondering if this is the correct behaviour. > > I'll just illustrate this with a quick example. The Tag model has a > single field, name. > > # starting with no tags >>>> Tag.objects.all() > [] > > # create a tag >>>> Tag.objects.create(name='one') > <Tag: one> > > # as expected >>>> Tag.objects.all() > [<Tag: one>] > > # assigning the QuerySet, as illustrated in documentation >>>> queryset = Tag.objects.all() > > # evaluate, by implicitly calling repr() >>>> queryset > [<Tag: one>] > >>>> Tag.objects.create(name='two') > <Tag: two> > > # expecting queryset to use cache, which does not contain new tag >>>> queryset > [<Tag: one>, <Tag: two>] > > # hmm, maybe not?? > > Any help on clarifying this would be greatly appreciated! > > David > > > >
The issue here is how __repr__ works on QuerySets, specifically it does repr(list(self[:MAX_REPR_SIZE])) that slicing causes it to create a new queryset, and so the result cache isn't populated in your QuerySet. 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 "Code can always be simpler than you think, but never as simple as you want" -- Me --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
