Hi Malcolm, Thanks very much for your help! I was (up until a few weeks ago) running off of the trunk, but I've stopped at an earlier revision (7922, I think). I kept updating but things kept breaking so I thought I'd just finalise the revision.
I did actually give it a go using Q objects yesterday, but it still seems to be generating the extra queries. I'll try updating to the latest Django release, then I will make sure for certain that there are only two queries being run for that particular aspect of the code. I'll let you know how I get on! Thanks again for your help. Regards, Mike. On Aug 26, 6:36 pm, Malcolm Tredinnick <[EMAIL PROTECTED]> wrote: > On Tue, 2008-08-26 at 08:05 -0700, [EMAIL PROTECTED] wrote: > > Hi guys, > > > I'm trying to optimize one of my views that is doing a rather (naive?) > > query like this: > > > ... > > post_stream = Post.objects.filter(poster=some_user) > > for other_user in other_user_queryset: > > post_stream = post_stream | Post.objects.filter(poster=other_user) > > ... > > [...] > > > The ORM generates a SQL query for each of the additional piped OR > > queries (this becomes a large number very quickly!). > > Which version of Django are you using? Because this isn't true for the > current subversion code. How are you determining that a query is run > esach time? > > Querysets are only evaluated when you first access their results and > "or"-ing together two querysets doesn't access the results, so it > constructs a single SQL query. The above loop should execute two > queries: one for the other_user_queryset (since you're accessing the > results there) and then one when you access the results of post_stream. > > A more concise, and probably clearer, way to write the above loop is to > use Q() objects: > > post_filter = Q(poster=some_user) > for user in other_queryset: > post_filter = post_filter | Q(poster=user) > post_stream = Post.objects.filter(post_filter) > > That's a little bit more lightweight at the Python level, since it's not > constructing and copying a QuerySet object each time around. From a > style point of view it's also focusing on constructing the filter, which > is the significant thing the loop does, rather than the queryset, which > is just a way to get at the results which are filtered. > > 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
