drf-prefetch-hint

The demo

One command. The whole answer.

Point it at a viewset. It reports every relation your serializer touches, what kind it is, how many queries it cost, and where in your code it came from — then hands you the ORM expression.

$ python manage.py prefetch_hint shop.views.AuthorViewSet --count 10

AuthorViewSet — 51 queries on 10 objects

  books.reviews         reverse FK   → prefetch_related
                          20 queries   shop/views.py:7
  books                 reverse FK   → prefetch_related
                          10 queries   shop/views.py:11
  publisher.name        FK           → select_related
                          10 queries   shop/views.py:10
  summary               method       → 10 queries, manual fix needed
                          10 queries   shop/views.py:12

  Add to get_queryset():

    .select_related("publisher")
    .prefetch_related(Prefetch("books", queryset=Book.objects.prefetch_related("reviews")))

  Projected: 51 → ~13 queries (estimate)

  Not auto-fixable:
    summary — SerializerMethodField runs arbitrary code

Real, selectable text — not a screenshot. Scroll the panel sideways on narrow screens.

The change

Before and after

class AuthorViewSet(viewsets.ReadOnlyModelViewSet):
    serializer_class = AuthorSerializer

    def get_queryset(self):
        return Author.objects.all()

from django.db.models import Prefetch
from shop.models import Author, Book

class AuthorViewSet(viewsets.ReadOnlyModelViewSet):
    serializer_class = AuthorSerializer

    def get_queryset(self):
        return (
            Author.objects.all()
            .select_related("publisher")
            .prefetch_related(
                Prefetch("books", queryset=Book.objects.prefetch_related("reviews"))
            )
        )

Internals

How it works

1. 01

   Wrap DRF’s get_attribute and to_representation; keep a ContextVar stack of the field currently resolving.

2. 02

   Django’s connection.execute_wrapper sees every query fire and tags it with whatever is on top of that stack — every query attributed to the exact serializer field that caused it.

3. 03

   Walk those field paths through model._meta to decide JOIN vs. second query.

4. 04

   Assemble the ORM expression and ast.parse-validate it before printing.

Everything runs inside a transaction that is always rolled back; DRF is left unpatched on every exit path including exceptions.

Honest limits

Limitations