Usage

Set extended manager to your models

from lookup_extensions.manager import Manager

class Article(models.Model):
    # ...

    objects = Manager()

Exists and Not exists

from django.db.models import Exists, OuterRef

tags = Tag.objects.filter(articles=OuterRef('id'), name='Tag 2')
Article.objects.filter(tag__exists=Exists(tags)).filter(author=self.au1)