Как наследовать serializer в Django REST Framework?

class Product(models.Model):
    name = models.CharField(max_length=256)
    price = models.PositiveIntegerField()
    image = models.ImageField(upload_to='products_images')

class ProductFile(BaseFileModel):
    product = models.ForeignKey(Product)
    file = models.FileField(upload_to='products_files')

class ProductFileSerializer(serializers.ModelSerializer):

    class Meta:
        model = ProductFile
        fields = ('file', )

class ProductSerializer(serializers.ModelSerializer):
    files = ProductFileSerializer(read_only=True)

    class Meta:
        model = Product
        fields = ('name', 'price', 'image', 'files')

    def create(self, validated_data):
        t = self._context['request'].data
        slug = Product.get_slug_by_name(validated_data['name'])
        product = Product.objects.create(slug=slug, **validated_data)
        
       # ВОТ ЭТО ДОЛЖНО РАБОТАТЬ, но в validated_data нет files :-(
        # files_data = validated_data.pop('files')
        # for data in files_data:
        #     ProductFile.objects.create(product=product, **data)

        return product