Using Django's QuerySet with Prefetching Returns Unexpectedly Large QuerySet Size
I'm deploying to production and I'm writing unit tests and I need some guidance on I'm working on a project and hit a roadblock... Quick question that's been bugging me - I'm working with an scenario with Django's `Prefetch` functionality when working with a related model... My models are set up with a ForeignKey relationship, and I'm trying to optimize my queries to avoid the N+1 question. When I use `prefetch_related`, I expect the number of records returned to be the same as the primary model's records, but I'm getting a much larger result set. 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=100) author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE) ``` Then, I execute the following query: ```python from django.db.models import Prefetch # Prefetching books for authors authors = Author.objects.prefetch_related(Prefetch('books')) ``` After running this, I check the count of the `authors` queryset and get a surprising result: ```python print(authors.count()) # Expected: number of authors ``` Instead of returning the number of authors, it seems to be returning a count that suggests it’s treating each author's books as separate entries. This leads me to believe there might be some misunderstanding on how `prefetch_related` actually functions. I’ve also tried using `distinct()` on the queryset, but it still yields a higher number than expected: ```python distinct_authors = authors.distinct().count() print(distinct_authors) ``` However, the result remains incorrect. Could someone guide to understand what I'm missing here? Is there a specific way I should be using `prefetch_related` to ensure I only get the distinct authors? I'm using Django version 3.2 and PostgreSQL as my database backend. Any insights would be greatly appreciated! This is part of a larger CLI tool I'm building. Am I missing something obvious? I'm working on a service that needs to handle this. Could this be a known issue? This issue appeared after updating to Python 3.10. I'd really appreciate any guidance on this.