Is it possible to use nested queries in Django ORM and how is it implemented?

Yes, in Django ORM, you can use nested queries called subqueries (Subquery). This allows executing queries where the result of one query is used inside another, which is useful for complex filtering and annotations.

To create a subquery, use the Subquery class from django.db.models. For example, you can select objects based on values from related models:

from django.db.models import OuterRef, Subquery

# Suppose there are models Author and Book, where Book is related to Author
latest_book = Book.objects.filter(author=OuterRef('pk')).order_by('-published_date')

authors = Author.objects.annotate(
    latest_book_title=Subquery(latest_book.values('title')[:1])
)

for author in authors:
    print(author.name, author.latest_book_title)

Here, OuterRef refers to the outer query, and Subquery inserts the subquery into the annotation. This way, you can efficiently build nested queries without writing raw SQL.