DRF update the nested foreign key of an object - django

Question

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"
}
}
model:
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)
serializer:
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",]
ViewSet:
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.
I was thinking of something like this:

Answer 1

Id field is what DRF make itself, and it's read-only by default
If you want to update that, you should override this field. Something like:
class ShipmentSerializer(serializers.ModelSerializer):
id = serializers.IntegerField()
name = serializers.CharField(read_only=True)
class Meta:
model = Shipment
fields = ["id", "name",]