> There is a threaded comments app http://code.google.com/p/django- > threadedcomments/ > , Now that I think about it, they surely would be doing this > conversion from relational to hierarchical format. I will read the > code and let you know if I can find something useful.
While I had been searching on djangosnippets.org, I had completely overlooked searching (properly) on Google; I completely missed this app. Thanks for the pointer! >> Hi folks, >> >> I'm somewhat new to Django, happily plodding along creating apps for >> a website, when I stumbled upon oddities when slicing QuerySets. I'm >> using 0.97pre (checked out from SVN about a month ago) on Mac OS X >> 10.4, Python 2.5. >> With the following very simply class: >> >> class Article(models.Model): >> text = models.CharField(max_length=100, default='lorem ipsum') >> def __unicode__(self): >> return self.text >> >> I can do the following: >>>>> from dtest.models import Article >>>>> for x in range(1, 5): >> ... a = Article(text='article no %d' % x) >> ... a.save() >> ... >>>>> articles = Article.objects.all() >>>>> for a in articles: >> ... print a >> ... >> article no 1 >> article no 2 >> article no 3 >> article no 4 >> >> That all works fine. Things get weird when I slice the QuerySet (I'm >> using the id-ing and type-ing to check on the object): >>>>> selection = Article.objects.all()[0:3] >>>>> print id(selection), type(selection) >> 20614928 <class 'django.db.models.query._QuerySet'> >>>>> for a in selection: >> ... print a >> ... >> article no 1 >> article no 2 >> article no 3 >> >>>>> selection = Article.objects.all()[0:3] >>>>> print id(selection), type(selection) >> 20627632 <class 'django.db.models.query._QuerySet'> >>>>> for i in range(4): >> ... print selection[i] >> ... >> article no 1 >> article no 2 >> article no 3 >> article no 4 >> >> ??? >> This is what I didn't expect: where's the IndexError (or >> ObjectNotFound)? >> >> But if I evaluate the selection before (using len(), to minimize >> output; print also works, for example), it does work as I expect: >>>>> selection = Article.objects.all()[0:3] >>>>> print id(selection), type(selection) >> 20615056 <class 'django.db.models.query._QuerySet'> >>>>> len(selection) >> 3 >>>>> print id(selection), type(selection) >> 20615056 <class 'django.db.models.query._QuerySet'> >>>>> for i in range(4): >> ... print selection[i] >> ... >> article no 1 >> article no 2 >> article no 3 >> Traceback (most recent call last): >> File "<console>", line 2, in <module> >> File "/sw/lib/python2.5/site-packages/django/db/models/query.py", >> line 161, in __getitem__ >> return self._result_cache[k] >> IndexError: list index out of range >> >> It obviously has to do with how and when QuerySets are evaluated; it >> looks like that before evaluation, the slice hasn't 'worked' yet. The >> id() and type() statements suggest it's still completely the same >> object though, before and after; nothing has apparently changed. >> (In fact, this is the reason I'm not recycling the first articles or >> selection QuerySet, but instead do an objects.all() each time; it >> gets evaluated in the first for-loop, and when recycled, things work >> as I expect). >> I found a few threads on the mailing list on this, bit I'm not sure >> if they explain this behaviour to me (threads referenced below). >> Could someone point me in the right direction/documentation on this, >> or just change how my mind works (nothing too drastically, please). >> Do I really need to evaluate the selection beforehand? >> Obviously, the example above is simplistic and should be done >> differently, but I do have a situation where I'd like to be able to >> index a sliced QueyrSet step by step, instead of iterating through >> it. Or, what possibly could also solve my problem: can I iterate >> through a (sliced) QuerySet step by step, by eg calling something >> like a next() method each time I needed the next element? (I've >> tried, but there's no next() method on QuerySets apparently). >> >> Thanks a lot, >> >> Evert >> >> http://groups.google.com/group/django-users/browse_thread/thread/ >> aef03c62f655fe45/a6ce6074ceab7438?lnk=gst&q=queryset >> +slicing#a6ce6074ceab7438http://groups.google.com/group/django- >> users/browse_thread/thread/ >> 3b98ffd38969c49a/a56354e0c0e61a9a?lnk=gst&q=queryset >> +slicing#a56354e0c0e61a9a > > --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
