Django Rest Framework Custom Field - Embedded on read / Primary Key on write

fields.py

from __future__ import unicode_literals
from django.core.exceptions import ObjectDoesNotExist
from rest_framework.relations import RelatedField


class EmbeddedPrimaryKeyRelatedField(RelatedField):
    default_error_messages = {
        'required': 'This field is required.',
        'does_not_exist': "Invalid pk '{pk_value}' - object does not exist.",
        'incorrect_type': 'Incorrect type. Expected pk value, received '
                          '{data_type}.',
    }

    def __init__(self, *args, **kwargs):
        self._serializer = kwargs.pop('serializer', None)()
        assert self._serializer is not None, \
            '`serializer` is a required argument.'
        super(EmbeddedPrimaryKeyRelatedField, self).__init__(*args, **kwargs)

    def to_internal_value(self, data):
        try:
            return self.get_queryset().get(pk=data)
        except ObjectDoesNotExist:
            self.fail('does_not_exist', pk_value=data)
        except (TypeError, ValueError):
            self.fail('incorrect_type', data_type=type(data).__name__)

    @property
    def fields(self):
        return self._serializer.fields

    def __iter__(self):
        for field in self._serializer:
            yield field

    def __getitem__(self, attr_name):
        return self._serializer[attr_name]

    def to_representation(self, data):
        return self._serializer.to_representation(data)
        
        
class PersonSerializer(serializers.ModelSerializer):

    company = EmbeddedPrimaryKeyRelatedField(many=True, queryset=Company.objects.all(), 
                                             serializer=CompanySerializer)

    class Meta:
        model = Person
        fields = ('name', 'company')