Prefetch_related for reverse relations in Django - Mini Project: Build & Apply

Prefetch_related for reverse relations in Django

📖 Scenario: You are building a simple Django app to manage authors and their books. Each author can have multiple books. You want to efficiently fetch authors along with all their books to display on a webpage.

🎯 Goal: Learn how to use Django's prefetch_related to fetch authors and their related books in one query, improving performance when accessing reverse relations.

📋 What You'll Learn

Create Django models for Author and Book with a reverse relation

Write a query to get all authors

Add a prefetch_related call to fetch related books

Access the prefetched books for each author without extra queries

💡 Why This Matters

🌍 Real World

Fetching related data efficiently is important in web apps to reduce database load and speed up page loading.

💼 Career

Understanding prefetch_related helps backend developers optimize Django queries and improve app performance.

1

Create Author and Book models with reverse relation

Create two Django models: Author with a name field, and Book with a title field and a foreign key to Author named author.

Django

# Define Author and Book models with fields
# Your code here

Need a hint?

Use models.ForeignKey with related_name='books' to create the reverse relation from Author to Book.

2

Write a query to get all authors

Write a Django query to get all Author objects and assign it to a variable called authors.

Django

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')

# Write a query to get all authors
# Your code here

Need a hint?

Use Author.objects.all() to get all authors.

3

Add prefetch_related to fetch related books

Modify the authors query to use prefetch_related('books') to fetch all related books for each author efficiently.

Django

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')

# Add prefetch_related to authors query
# Your code here

Need a hint?

Use prefetch_related('books') on the Author.objects query.

4

Access prefetched books for each author

Write a loop to go through each author in authors and access their related books using the reverse relation author.books.all().

Django

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')

authors = Author.objects.prefetch_related('books').all()

# Loop through authors and access their books
# Your code here

Need a hint?

Use a for loop with author in authors and get books with author.books.all().