Django select objects with empty ManyToManyField

Question

Considering the following models, knowing a family, how do I select Kids with no buyers?

class Family...

class Kid(models.Model):
    name = models.CharField(max_length=255)
    family = models.ForeignKey(Family)
    buyer = models.ManyToManyField(Buyer, blank=True, null=True)

family = get_object_or_404(Family, pk=1)
for_sale = family.kid_set.filter(buyer... this screws my child trade business

Answer 1

family.kid_set.filter(buyer__isnull=True) should work.

Answer 2

@piquadrat's answer is correct. You can also do:

for_sale = Kid.objects.filter(family__pk = 1, buyer = None)

This lets you avoid a separate query to look up the Family instance.