Django rest嵌套序列化程序不显示字段

# models.py
class Author(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

# serializers.py
class AuthorSerializer(serializers.ModelSerializer):
    class Meta:
        model = Author
        fields = ['name', 'age']

class BookSerializer(serializers.ModelSerializer):
    author = AuthorSerializer()

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

# views.py
class BookView(APIView):
    serializer_class = BookSerializer

    def get(self, request):
        books = Book.objects.all()
        serializer = self.serializer_class(books, many=True)
        return Response(serializer.data)