👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-12

django orm prefetch_related Python

I'm trying to configure I'm updating my dependencies and I've been researching this but I'm confused about I'm deploying to production and I'm working on a project and hit a roadblock... I'm working with a frustrating scenario with Django when trying to filter queryset results based on a related field that I've prefetched. I have two models, `Author` and `Book`, where a `Book` has a foreign key to `Author`. In a view, I'm trying to retrieve all books by authors who meet certain criteria, but I'm getting a `RelatedObjectDoesNotExist` behavior while accessing a field from the prefetched authors. Here's a simplified version of my models: ```python class Author(models.Model): name = models.CharField(max_length=100) class Book(models.Model): title = models.CharField(max_length=200) author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE) ``` In my view, I'm trying to do the following: ```python from django.shortcuts import render from .models import Book def book_list(request): books = Book.objects.prefetch_related('author').filter(author__name='John Doe') return render(request, 'books/list.html', {'books': books}) ``` However, when I access `book.author.name` in my template, I sometimes get this behavior: ``` RelatedObjectDoesNotExist: Author has no related Author matching the query ``` I've confirmed that there are indeed authors with the name 'John Doe' in the database, so I'm puzzled as to why this is happening. It seems like Django is attempting to access an author that doesn't exist for some of the book entries. As a workaround, I tried adding a `.distinct()` to my query, but that didn't help. I've also checked the database for any inconsistencies, and everything seems correct. Am I missing something in my queryset or the way I'm handling the prefetched data? Any insights would be appreciated! Is there a better approach? The stack includes Python and several other technologies. Any advice would be much appreciated. I'm on macOS using the latest version of Python. Is this even possible? Any help would be greatly appreciated! This issue appeared after updating to Python 3.9. Hoping someone can shed some light on this.