On Sat, 2006-07-22 at 19:43 +1000, Matthew Flanagan wrote:
> Hi,
>
> I have the following simplified models. Then I create a number of IP
> addresses and interfaces, with not all IP addresses being related to
> an interface.
>
> class IPAddress(models.Model):
> address = models.CharField(maxlength=15)
>
> class Admin: pass
>
> class Interface(models.Model):
> name = models.CharField(maxlength=15)
> ipaddress = models.ForeignKey(IPAddress)
>
> class Admin: pass
>
> Then when I try:
>
> >>> IPAddress.objects.filter(interface__isnull=False)
>
> I get a list of IPAddresses that have related interfaces.
>
> Then if I try:
>
> >>> IPAddress.objects.filter(interface__isnull=True)
>
> I get an empty list when I expected to be getting the IP addresses
> that are not related to any interfaces. Right?
>
> Ultimately I'd like to do this:
>
> class Interface(models.Model):
> name = models.CharField(maxlength=15)
> ipaddress = models.ForeignKey(IPAddress,
> limit_choices_to={'interface__isnull':True})
>
> class Admin: pass
>
> so that the admin will only should "free" ip addresses not ones that
> ae already used.
>
> Is this a bug? Am I doing the wrong lookup?
It's not a bug. But it could be argued it's a missing feature. Because
the reverse relation does not exist yet, you cannot query against it. We
would need to special case this type of situation. For the moment, you
will need to construct a custom SQL query if you want to do this (it's
not too painful).
If there's not a ticket for it already (it came up in [1]), maybe file
an enhancement request.
[1]
http://groups.google.com/group/django-users/browse_frm/thread/98b7aedf8f9d806c/385833fa2b597afe?lnk=gst&rnum=1#385833fa2b597afe
Regards,
Malcolm
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