how to subquery in queryset in django?

The correct answer on your question is here https://docs.djangoproject.com/en/2.1/ref/models/expressions/#subquery-expressions

As an example:

>>> from django.db.models import OuterRef, Subquery
>>> newest = Comment.objects.filter(post=OuterRef('pk')).order_by('-created_at')
>>> Post.objects.annotate(newest_commenter_email=Subquery(newest.values('email')[:1]))

as mentioned by ypercube your use case doesn't require subquery.

but anyway since many people land into this page to learn how to do sub-query here is how its done.

employee_query = Employee.objects.filter(company='Private').only('id').all()
Person.objects.value('name', 'age').filter(id__in=employee_query)

Source: http://mattrobenolt.com/the-django-orm-and-subqueries/

ids = Employee.objects.filter(company='Private').values_list('id', flat=True)
Person.objects.filter(id__in=ids).values('name', 'age')