Solved (in Django 1.1):
tags = Tag.objects.annotate(num_pages=Count('page')).filter
(num_pages__gt=0)
On 9 Jan., 19:50, janedenone <janeden...@googlemail.com> wrote:
> I defined two models (Tag and Page), where the Page model links to the
> Tag model:
>
> tags = models.ManyToManyField(Tag, blank=True)
>
> For a single tag, I can refer to the pages linked to that tag like so:
>
> for page in tag.page_set:
> ...
>
> results = tag.page_set.count()
>
> But I cannot find a way to obtain a list of tags where each tag is
> linked to at least one page. My attempt
>
> tags = Tag.objects.filter(page_set__count__gt=0)
>
> results in an error: Django complains that the field 'page_set' is
> unknown. Why can I use page_set as a 'virtual' tag property (even
> though this set is not defined in the model), and how can I refer to
> the page_set in a query?
>
> Many thanks,
> Jan
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