def METHOD_NAME(self):
    if not self.author:
        return
    qs = self.author.collections.using('default')
    slugs = {slug: id for slug, id in qs.values_list('slug', 'id')}
    if self.slug in slugs and slugs[self.slug] != self.id:
        for idx in range(len(slugs)):
            new = f'{self.slug}-{idx + 1}'
            if new not in slugs:
                self.slug = new
                return