Sorry for the delay. hosts__isnull works!
But i can confirm exclude doesn't:
h = Host.objects.create(ip="0.0.0.0")
d = RegisteredDomain.objects.all()[0]
d.hosts.add(h)
RegisteredDomain.objects.count()
--> 477L (total)
RegisteredDomain.objects.filter(hosts=None).count()
--> 476L (good!)
RegisteredDomain.objects.exclude(hosts=None).count()
--> 0 (not so good :-/)
RegisteredDomain.objects.filter(hosts__isnull=False).count()
--> 1L (good!)
I will paste you both models to be sure:
class Host(TimeStampedModel):
ip = models.IPAddressField(unique=True)
class RegisteredDomain(TimeStampedModel):
domain = models.CharField(max_length=255, unique=True)
spam_time = models.DateTimeField(null=True)
hosts = models.ManyToManyField(Host,
related_name="registered_domains")
random = models.BooleanField(null=True)
Is this a bug or i just didn't get how models work? :-)
Riccardo
On 4 Mai, 21:22, Malcolm Tredinnick <malc...@pointy-stick.com> wrote:
> On Mon, 2009-05-04 at 09:18 -0700, Riccardo Pelizzi wrote:
> > Hello,
>
> > I have a model which looks kinda like this:
>
> > class Host(model):
> > ip = IPAddressField()
>
> > class Domain(model):
> > hosts = ManyToManyField(Host)
>
> > If i want to get all the domains without hosts:
> > Domain.objects.filter(hosts=None)
> > works.
>
> > Later on in my script i need to get the opposite, all the domains
> > having one or more hosts associated. using exclude instead of filter
> > with the same condition doesn't work as expected (at least as I
> > expected :-P), it just returns an empty queryset. Is there a way to
> > formulate thequeryusing the django api? or should i use custom sql?
>
> That should work properly. It works for me using exactly your models
> with a few different Host/Domain combinations.
>
> The SQL we currently generate for Domain.objects.exclude(hosts=None) is
> a little inefficient, but it's not fundamentally incorrect. It just uses
> a couple more tables than it needs to be because the "NULL" case can
> take advantage of one particular extra optimisation that isn't in the
> code yet. I'm surprised it isn't returning the correct result.
>
> Another to get the same answer, which generates simpler SQL but is
> potentially a little less efficient on the database side is
>
> Domain.objects.filter(hosts__isnull=False).distinct()
>
> That's essentially the only case where Django has a "not" filter
> available: you can actually filter for "not NULL". The distinct() call
> there is important, as for many-to-many fields, you would otherwise get
> back one domain object for every host (so repetitions for domains with
> multiple hosts), not just the set of domains that have at least one
> host.
>
> In any case, I suspect there's something else going on in your
> particular case, as the SQL generated should be pulling back the results
> you're after and it works with a small example using your models. If you
> can use those models, as pasted, to generate an incorrect result, what
> is the smallest amount of data (Host & Domain objects) you need to
> create to demonstrate the problem. That would be interesting to see.
>
> Regards,
> Malcolm
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