I was able to track down the problem a little further and I saw that
Tag.objects.get_for_model(Note, 'foo') |
Note.objects.filter(tag='bar')
results in a:
"Cannot combine a unique query with a non-unique query"
exception.
Does anybody have any idea what that means? What is a unique query?
On May 22, 7:08 pm, omat <[EMAIL PROTECTED]> wrote:
> An other case where I get empty result sets unexpectedly is when I
> want to join 2 querysets, one holding the objects that the current
> user entered and the other holds the objects marked as favorite by the
> current user.
>
> I have a manager for Favorite objects that takes the model and the
> user and returns a queryset for that model that are marked as
> favorites by the given user:
>
> class FavoriteManager(models.Manager):
> def get_by_user(self, Model, user):
> ctype = ContentType.objects.get_for_model(Model)
> rel_table = qn(self.model._meta.db_table)
> return Model._default_manager.extra(
> tables=[self.model._meta.db_table], # Use a non-explicit join
> where=[
> '%s.content_type_id = %%s' % rel_table,
> '%s.user_id = %%s' % rel_table,
> '%s.%s = %s.object_id' % (qn(Model._meta.db_table),
> qn(Model._meta.pk.column),
> rel_table)
> ],
> params=[ctype.id, user.id],
> )
>
> And when called like this:
> Favorite.objects.get_by_user(Note, user)
>
> the result is a QuerySet containing Note objects which are favorites
> of the given user. The structure of the QuerySet is exactly the same
> as the result of a query set generated by Note.objects.
>
> But when I try to get the union such as
>
> Note.objects.all() | Favorite.objects.get_by_user(Note, user)
>
> The result is a QuerySet objects with no elemnts in it.
>
> Thanks...
>
> On May 22, 4:38 pm, omat <[EMAIL PROTECTED]> wrote:
>
> > Hi,
>
> > The "bitwise or" ('|') works fine when taking the union of query sets
> > such as:
> > Note.objects.filter(tag='foo') | Note.objects.filter(tag='bar')
>
> > But the result of following is an EmptyQuerySet object:
> > Note.objects.filter(tag='foo') | Note.objects.none()
>
> > Shouldn't it be equivalent to Note.objects.filter(tag='foo'). Am I
> > missing something?
>
> > Thanks,
> > omat
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