DRF обновление вложенного внешнего ключа объекта

I am trying to wrap my head around this for too long already :( I need the following output for my frontend (specially the ID & name field in combination):

{ "serial": "e3461fb0", "shipment": { "id": 1, "name": "via rotterdam" } }

модель:

class Shipment(models.Model):
    name = models.CharField("name", max_length = 128)
    date = models.DateField()

class Product(models.Model):
    serial = models.CharField("serial", max_length = 31, unique = True)
    shipment = models.ForeignKey(Shipment, on_delete = models.CASCADE, blank = True, null = True)

сериализатор:

class ShipmentSerializer(serializers.ModelSerializer):
    class Meta:
        model = Shipment
        fields = ["id", "name",]
        
class ProductSerializer(serializers.ModelSerializer):
    shipment = ShipmentSerializer()

    def update(self, instance, validated_data):
        print("TEST:", instance, validated_data)
        return super().update(instance, validated_data)

    class Meta:
        model = Product
        fields = ["serial", "shipment",]    
        lookup_field = "serial"
        read_only_fields = ["serial",]

Видовой набор:

class ProductViewSet(ModelViewSet):
    serializer_class = ProductSerializer
    lookup_field = "serial"
    http_method_names = ["get", "patch", "put"]

    def get_queryset(self):
        return Product.objects.all()

my problem here is the following: Lets say a product ist linked to a shipment and what I want now is to update that product by linking it to another shipment by using the id. But even in the HTML view of DRF I only get to see the name attribute of shipment. How can I only show/use the id here? I know I could modify the __str__ method of the model to return a string representation and split it later in the frontend, but I would like to avoid that if possible.

Я думал о чем-то подобном:

class ShipmentSerializer(serializers.ModelSerializer):
    id = serializers.IntegerField()
    name = serializers.CharField(read_only=True)

    class Meta:
        model = Shipment
        fields = ["id", "name",]