👀 Views: 76 💬 Answers: 1 📅 Created: 2025-06-14

django database prefetch_related Python

I'm experiencing an unexpected issue with Django's `prefetch_related` method when trying to optimize my queries for a product catalog. I have two models, `Category` and `Product`, where a `Category` can have many `Products`. When I fetch categories along with their products using `prefetch_related`, I notice some categories return an empty list for their products even though they should have associated products in the database. Here’s the relevant part of my models: ```python class Category(models.Model): name = models.CharField(max_length=100) class Product(models.Model): name = models.CharField(max_length=100) category = models.ForeignKey(Category, related_name='products', on_delete=models.CASCADE) ``` I'm running Django 3.2 and using PostgreSQL as my database. Here’s the code I used to fetch the categories: ```python categories = Category.objects.prefetch_related('products').all() for category in categories: print(category.name, category.products.all()) ``` The output sometimes shows categories with names but an empty list for products, which is perplexing as I know there are products tied to those categories. I’ve checked the database directly and confirmed the relationships exist. I've also tried using `select_related` instead of `prefetch_related`, but that led to a different set of issues, primarily related to performance on larger datasets. Is there a specific scenario or edge case with `prefetch_related` that could lead to these inconsistent results? What am I missing here? Any insights or suggestions would be greatly appreciated!