Django REST Framework: create and update an object

I have two models one Country and one Office model. The office model has a ForeignKey to the Country model:

class Country(TranslatableModel):
    iso = models.CharField(
        max_length=2, verbose_name=_('iso code'),
        help_text="ISO 3166 ALPHA-2 code")
    translations = TranslatedFields(
        name=models.CharField(max_length=100, verbose_name=_('name')),
    )



class Office(models.Model):
    country = models.ForeignKey(
        Country, related_name='country', verbose_name=_('country'))

Now I want to write a django-rest-framework-serializer to send simply {"country": "us"} to get a ForeingKey to the Country Model.

How can I achieve this?

Read-only

To simply send that representation to the client (read-only, not dealing with creating objects from their deserialized representation)

class OfficeSerializer(serializers.ModelSerializer):
    country = serializers.Field(source='country.iso') # this field of the serializer
                                                      # is read-only

As you can see, it'll read will read country.iso from your office instance, which resolves to 'us' e.g., then gets put into a serializer key called 'country', given you an output of {'country': 'us'}

Writable nested field

Now to complete this, let's write a custom OfficeSerializer.create():

def create(self, validated_data):
    # This expects an input format of {"country": "iso"}

    # Instead of using the ID/PK of country, we look it up using iso field
    country_iso = validated_data.pop('country')
    country = Country.objects.get(iso=country_iso)

    # Create the new Office object, and attach the country object to it
    office = Office.objects.create(country=country, **validated_data)

    # Notice I've left **validated_data in the Office object builder,
    # just in case you want to send in more fields to the Office model

    # Finally a serializer.create() is expected to return the object instance
    return office

As for a OfficeSerializer.update() it's similar:

def update(self, instance, validated_data):
    # instance is your Office object
    # You should update the Office fields here
    # instance.field_x = validated_data['field_x']

    # Let's grab the Country object again

    country_iso = validated_data.pop('country')
    country = Country.objects.get(iso=country_iso)

    # Update the Office object
    instance.country = country
    instance.save()

    return instance