David North

You can now sign in to leave comments here (yes, dear readers, both of you!) – using an OpenID if you have one, and in related news, I’ve got m’self a shiny new OpenID to go and do likewise on other people’s sites.

a.k.a. “How to query for all objects not in a given subclass”

I ran across this problem today – do please leave a comment if you know of a better way to solve it than what follows.

You have two Django models, one of which inherits from the other, e.g.:

class Order(models.Model):
    # some fields

class DiningOrder(Order):
    # some more fields

So, how do I write a query (using the Django ORM) which returns all the Orders which are not DiningOrders?

Apparently, this does the trick:

>>> Order.objects.all().count()
762L
>>> DiningOrder.objects.all().count()
93L
>>> Order.objects.exclude(id__in=[d.id for d in DiningOrder.objects.all()]).count()
669L

My main problem with RSS readers is that if I go away for a few days and come back, I don’t really have time to catch up with all the posts which came up whilst I was away. What I needed, therefore, was a stateless reader which would just show the newest 10 entries or so.

Add in category filtering and a web interface – such as it is – and you get Bogroll, which I’ve just released under the GPL. You can grab the 0.1 release, check out the code from subversion, and have a nosey at my installation.

Incidentally, if anyone can think of a better name for it, do get in touch.