👀 Views: 86 💬 Answers: 1 📅 Created: 2025-06-08

django modelmanager queryset Python

I've looked through the documentation and I'm still confused about I'm integrating two systems and I'm working on a project and hit a roadblock... I'm experiencing an scenario with a custom `ModelManager` in Django that isn't filtering records as expected. I have a model `Book` that has a foreign key relationship to another model `Author`. I created a custom manager to filter books by a specific author, but when I call this manager method, it doesn't return the expected results. Here's how my models look: ```python from django.db import models class Author(models.Model): name = models.CharField(max_length=100) class Book(models.Model): title = models.CharField(max_length=200) author = models.ForeignKey(Author, on_delete=models.CASCADE) class BookManager(models.Manager): def by_author(self, author_id): return self.filter(author__id=author_id) class BookWithManager(Book): objects = BookManager() ``` I have added some books and authors in my database. However, when I try to fetch books by a specific author like this: ```python books = BookWithManager.objects.by_author(1) print(books) ``` I expect to see all the books written by the author with ID 1, but it returns an empty queryset: ``` <QuerySet []> ``` I've double-checked that the author with ID 1 exists, and the foreign key in the `Book` table is set correctly. I also tried using the default manager directly: ```python books = Book.objects.filter(author__id=1) print(books) ``` This returns the expected books, so it seems the scenario is with my custom manager. I suspect it might be related to how the related `author` field is being accessed in the manager, but I need to find a solution. Any insights into what might be going wrong here would be greatly appreciated! Thanks for taking the time to read this!