Should be doable but you need to filter on a field of the subclass
being null.

SomeModel.objects.filter(somemodelsubclass__somefield=None) ,
somefield cannot be id or pk.

On 27 Feb, 14:13, Calvin Spealman <[email protected]> wrote:
> On Fri, Feb 27, 2009 at 1:31 AM, Malcolm Tredinnick
>
>
>
> <[email protected]> wrote:
>
> > On Thu, 2009-02-26 at 11:08 -0500, Calvin Spealman wrote:
> >> I'm looking for the best way to query based on the existence of an
> >> instance of a subclass. In my case, there are Actions that have
> >> several subclasses, like FriendRequest, PhotosTagged, etc. The user
> >> has selected a set of types they are interested in, so I need to query
> >> for all the actions that are instances of one of these particular
> >> subclasses. I could query for all, and then filter on the python-side,
> >> but that is what I'm looking to avoid. Is there a way to do this from
> >> the query api. If there isn't, what would one look like and would it
> >> be accepted?
>
> > This is a "how do I....?" sort of question. The best place to ask those
> > is the django-users mailing list. This list is for the internal
> > development of Django itself.
>
> I ask here because I've already exhausted user forums and determined
> the answer is "You can't do that", so now I'm looking for if changes
> to allow such a query would be allowed, or very easy to add.
>
> --
> Read my blog! I depend on your acceptance of my opinion! I am 
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