Avoid the N+1 problem in DRF

The N+1 problem is a common issue that can occur when using the Django REST framework serializer. It happens when the code makes multiple database queries to retrieve related data, instead of using a single query with a JOIN statement.

One way to fix this issue is by using the select_related and prefetch_related methods on your queryset. These methods allow you to specify which related data should be fetched in a single database query, reducing the number of queries needed.

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from django.db import models

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

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)


books = Book.objects.all()
for book in books:
    print(book.author.name) 


books = Book.objects.select_related('author').all()
for book in books:
    print(book.author.name)

select_related is used for one-to-one and many-to-one relationships while prefetch_related is used for one-to-many and many-to-many relationships.