What is the process for making a double nested serializer in Django?

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To make a double nested serializer in Django, you need to create two serializers and nest one within the other. Here are the general steps:

1. Determine the model relationships: Identify which models are related to each other and how they are related.

2. Create the inner serializer: Write a serializer that represents the innermost model in the relationship. This serializer will need to include any fields that you want to serialize from the model.

3. Create the outer serializer: Write a serializer that represents the model that is one level above the innermost model. This serializer will include the inner serializer as a field.

4. Nest the inner serializer: In the outer serializer, include the inner serializer as a field. Use the source argument to specify the relationship between the models that the inner serializer represents.

5. Test the serializer: Serialize some data using the outer serializer and ensure that the output is what you expect.

Here's some sample code that demonstrates the steps above:

from rest_framework import serializers
from .models import Author, Book, Chapter

# Step 2: Inner serializer
class ChapterSerializer(serializers.ModelSerializer):
    class Meta:
        model = Chapter
        fields = ['title', 'text']

# Step 3: Outer serializer
class BookSerializer(serializers.ModelSerializer):
    chapters = ChapterSerializer(many=True, read_only=True)

    class Meta:
        model = Book
        fields = ['title', 'author', 'published_at', 'chapters']

# Step 4: Nest the inner serializer
class AuthorSerializer(serializers.ModelSerializer):
    books = BookSerializer(many=True, read_only=True)

    class Meta:
        model = Author
        fields = ['name', 'birth_date', 'nationality', 'books']

In this example, we have three models: Author, Book, and Chapter. An author can write multiple books, and a book can have multiple chapters. The AuthorSerializer is the outer serializer and includes the BookSerializer, which is the inner serializer, as a field. The BookSerializer includes the ChapterSerializer as a field using the chapters attribute.