Django-Rest-Framework. Updating nested object

This is the way I’ve accomplished the task:

I’ve added an id field to the InvoiceItemSerializer

class InvoiceItemSerializer(serializers.ModelSerializer):
    ...
    id = serializers.IntegerField(required=False)
    ...

And the update method for the InvoiceSerializer

def update(self, instance, validated_data):
    instance.nr = validated_data.get('nr', instance.nr)
    instance.title = validated_data.get('title', instance.title)
    instance.save()

    items = validated_data.get('items')

    for item in items:
        item_id = item.get('id', None)
        if item_id:
            inv_item = InvoiceItem.objects.get(id=item_id, invoice=instance)
            inv_item.name = item.get('name', inv_item.name)
            inv_item.price = item.get('price', inv_item.price)
            inv_item.save()
        else:
            InvoiceItem.objects.create(account=instance, **item)

    return instance

Also in the create method I’m popping the id if it is passed.