Efficiently delete orphaned m2m objects/tags in Django

Question

I have two models - Photo and Tag - which are connected via a ManyToManyField.

class Photo(models.Model):
    tags = models.ManyToManyField(Tag)

class Tag(m         


        

Answer 1

Try sub-query w/ intermediate table

qs = Tag.objects.exclude(pk__in=Book.tags.through.objects.values('tag'))

# then you could
qs.delete()

# or if you need to trigger signal per item
for x in qs:
    x.delete()