prefetch_related for M2M
Batch-load many-to-many data efficiently.
prefetch_related for M2M is a free Django Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Django Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Meet prefetch_related
prefetch_related handles the relationships a join cannot, like many-to-many and reverse links, with smart batching. 📦
Two Queries, Not Many
Instead of one giant join, it runs a second query for the related rows, then matches them up in Python.
The Basic Call
Pass the relation name to prefetch_related, just like before, and Django batches the lookups for you automatically.
authors = Author.objects.prefetch_related('books')Why Two Beats N+1
One query for authors and one for all their books is two trips total, no matter how many authors you loop over.
for author in authors:
print(author.books.count())Best for Many
Reach for it whenever each object links to multiple rows: many-to-many fields and reverse foreign keys are perfect fits.
Reverse Relations Work
It shines on reverse accessors, like an author reaching all their books, where select_related simply cannot help.
Mixing Both Tools
You can chain both optimizers on one queryset, using each for the relationship type it handles best.
Book.objects.select_related('author').prefetch_related('tags')Control with Prefetch
The Prefetch object lets you filter or order the related rows that get fetched, giving you fine control.
from django.db.models import Prefetch
Author.objects.prefetch_related(
Prefetch('books', queryset=Book.objects.filter(year=2024)))Done in Python
The matching happens in Python, not SQL. That is why it sidesteps the row explosion a big many-to-many join would cause.
Filter Inside the Loop Carefully
Calling filter on a prefetched set inside a loop fires fresh queries again. Use Prefetch to keep the batching benefit.
Two Tools, One Goal
select_related for single links, prefetch_related for many. Together they crush N+1 in almost any view. 🚀
Quick Check
Choose the right optimizer for this case.
Recap
prefetch_related batches many-to-many and reverse links into a second query, matched in Python. Pair it with select_related for full coverage. ✅
Frequently asked questions
Is the “prefetch_related for M2M” lesson free?
Yes — the full text of “prefetch_related for M2M” is free to read here on the web, and the Django Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Django Academy course, upgrade to CoddyKit PRO.
What will I learn in “prefetch_related for M2M”?
Batch-load many-to-many data efficiently. You practise Django Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Django Academy?
No prior experience is required. Django Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “prefetch_related for M2M” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Django Academy lesson?
Yes. Every Django Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Spotting the N+1 Problem
- select_related for Foreign Keys
- prefetch_related for M2M
- Profiling with Debug Toolbar