👀 Views: 25 💬 Answers: 1 📅 Created: 2025-07-03

django queryset custom-manager Python

I'm not sure how to approach I'm using Django 4.0 and I've defined a custom model manager for my `Book` model. The goal is to filter books by their availability status. Here’s what I have: ```python from django.db import models class BookManager(models.Manager): def available(self): return self.filter(is_available=True) class Book(models.Model): title = models.CharField(max_length=200) is_available = models.BooleanField(default=True) objects = BookManager() ``` When I call `Book.objects.available()`, I expect to get a queryset of available books. However, I'm working with a situation where it sometimes returns `None` instead of a queryset, especially after performing bulk updates on the model. Here’s the code I use to make the bulk update: ```python Book.objects.update(is_available=False) ``` After running this update, if I immediately call `Book.objects.available()`, it sometimes returns `None`. I’ve tried calling `refresh_from_db()` on instances of `Book`, but it doesn’t seem to resolve the scenario. I also verified that the database is correctly updated, and calling `Book.objects.all()` shows the expected results. I suspect it might be related to how Django caches querysets or something related to database transactions, but I’m not sure how to troubleshoot this effectively. Can anyone provide insights or solutions for this scenario? I’d appreciate any pointers on debugging this behavior! What's the correct way to implement this? The project is a mobile app built with Python. Any ideas what could be causing this?