gistfile1.txt

    def get_toplevel_categories(self, **filters):
        """
        Similar to objects.filter but returns only toplevel results.

        Example:
        Category.objects.get_toplevel_categories(categorysubset__sites__exact=settings.SITE_ID)
        """

        #Filter categories based on the filter keyword argument
        category_subset = self.filter(**filters)

        #Now let's fetch their corresponding parents and intersections
        top_level_categories = category_subset.filter(models.Q(parent=None) | ~models.Q(parent__in=category_subset)).distinct()

        #If there are no top level categories, it's most likely because subsets have not been set up yet,
        #in which case we want all of top level categories.  This will prevent the primary_category field from showing up blank
        #for unit tests and when there are not subsets defined.
        if top_level_categories.count()==0:
            top_level_categories = self.filter(parent=None)
        return top_level_categories