Django Rest Framework: Unexpected `None` Values in Serializer Output When Using Nested Serializers
I'm currently working on a Django Rest Framework (DRF) application where I'm trying to serialize a model with nested relationships. However, I'm encountering an issue where some fields in the output are unexpectedly returning `None` instead of the expected data. 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=200) author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE) ``` For the serializer, I'm using nested serializers: ```python from rest_framework import serializers class AuthorSerializer(serializers.ModelSerializer): class Meta: model = Author fields = ['name'] class BookSerializer(serializers.ModelSerializer): author = AuthorSerializer() class Meta: model = Book fields = ['title', 'author'] ``` When I try to serialize a `Book` instance, using the following code: ```python book = Book.objects.get(pk=1) serializer = BookSerializer(book) print(serializer.data) ``` I expect the output to include the author's name, but sometimes it returns: ```json { "title": "Some Book Title", "author": null } ``` I've verified that the `author` field is correctly set on the `Book` instance, and the relevant `Author` instance exists in the database. I've also tried using `.select_related('author')` in my query to optimize, but it doesn't seem to change anything. Additionally, I've checked for any overridden `to_representation` methods in my serializers that might be affecting the output, but found none. Could this be an issue related to the way related fields are fetched or serialized in DRF? Any insights or suggestions on how to ensure that the author data is always included would be greatly appreciated!