Hi,
On 28 Okt., 10:56, Daniel Roseman <[EMAIL PROTECTED]>
wrote:
> On Oct 28, 9:33 am, janedenone <[EMAIL PROTECTED]> wrote:
>
>
>
> > Hi,
>
> > I need to exclude certain elements from a QuerySet. My models look
> > like this (simplified):
>
> > class Author(models.Model):
> > first_name = models.CharField(max_length=90, blank=True)
> > last_name = models.CharField(max_length=90, blank=True)
>
> > class Page(models.Model):
> > author = models.ForeignKey(Author)
> > mother = models.ForeignKey('self', blank=True, null=True,
> > related_name='child_set')
>
> > For each author, I need to get the set of pages representing all top-
> > level works by that author (so I don't need the chapters, sections
> > etc.). I guess the solution looks something:
>
> > def _get_top_level_children(self):
> > return self.page_set.exclude(author=mother.author)
> > top_level_children = property(_get_top_level_children)
>
> > Obviously, it does not work like this. How can I limit the queryset to
> > all entries where the 'author' object of a page does not match the
> > 'author' object of the page's 'mother' object?
>
> > Kind regards,
> > Jan
>
> Well the only thing wrong with your code is you need a self in there -
> author=self.mother.author
Many thanks, but the method above is a method of Author objects, so
self refers to the current author. I need to get all elements (pages)
written by that author if (and only if) the parent page has a
different author. The literal SQL would be something like:
SELECT pages.id, pages.author_id, motherpages.author_id AS
motherauthor
FROM pages, pages AS motherpages
WHERE motherpages.page_id = pages.mother_id
AND pages.author_id = 1234
AND pages.author_id <> motherpages.author_id
> But I wouldn't do it like that. If you just want all top-level Page
> objects, you could do
> Page.objects.filter(mother__isnull=True)
>
> and if you want all top-level Pages belonging to a particular author,
> it would be
> author.page_set.filter(mother__isnull=True)
Sorry, that was misleading – I need all pages heading a sub-tree
written by the same author. These pages are not necessarily top-level
pages.
>
> (BTW in English we would usually say 'parent' rather than 'mother'...)
Thanks – the name "mother" was chosen for historical reasons.
Cheers,
Jan
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