[Django Rest Framework] Serializer for a PrimaryKeyRelatedField where we use a unique key instead of the primary key.

serializers.py

class ModelA(models.Model):
    attr1 = models.Charfield()
    attr2 = models.Charfield(unique=True)


class ModelB(models.Model):
    foreign = models.ForeignKey(ModelA)


class OtherFieldUniqueSerializer(serializers.PrimaryKeyRelatedField):
    
    def from_native(self, value):
        try:
            return ModelA.objects.get(attr2=value)
        except ObjectDoesNotExist:
            raise ValidationError(self.error_messages['does_not_exist'])
        except (TypeError, ValueError):
            raise ValidationError(self.error_messages['incorrect_type'])

    def to_native(self, obj):
        return obj.attr2


class ModelBSerializer(serializers.ModelSerializer):
    foreign = OtherFieldUniqueSerializer('attr2')

    class Meta:
        model = ModelB
        fields = ('id', 'foreign', )