👀 Views: 47 💬 Answers: 1 📅 Created: 2025-06-12

django bulk-update prefetch-related performance Python

I'm attempting to set up Hey everyone, I'm running into an issue that's driving me crazy. I'm working on a Django 4.1 project where I need to bulk update a related model based on the values from the main model. I have two models, `Author` and `Book`, where an `Author` can have multiple `Book` instances. After fetching the authors along with their books using `prefetch_related`, I want to update all books for a specific author in a single query. However, I'm running into issues where changes don't reflect immediately in the database, and I'm also concerned about performance. Here's a snippet of what I'm trying: ```python from django.db import transaction from .models import Author, Book @transaction.atomic def update_books_for_author(author_id, new_title): author = Author.objects.prefetch_related('books').get(id=author_id) for book in author.books.all(): book.title = new_title # Trying to bulk update but seems ineffective Book.objects.bulk_update(author.books.all(), ['title']) ``` When I run this function, I expect all books related to the author to be updated with the new title. However, when I check the database afterwards, the titles remain unchanged. Additionally, I received a warning that some books might not have been updated due to the current transaction state. I've also tried using `update()` directly on the queryset, but this approach doesn't suit my need to dynamically change the titles based on some operation. Any advice on what I'm doing wrong or how I can achieve this more efficiently would be appreciated. My development environment is macOS. Thanks in advance! I'm developing on Windows 10 with Python. Could this be a known issue?