How to get object instance inside to_internal_value()?

[Rahul Sarma]

Hi, I am writing a custom field. I am doing validation inside the to_internal_value() method for which I need the object instance. I'm able to get it in the to_representation() method as "value" argument. How do I also access it inside the to_internal_value() method?

class OptionField(serializers.Field):

    def to_representation(self, value):
        selected_options = Option.objects.filter(
                optiongroup__question=value).distinct()
        return OptionSerializer(selected_options, many=True).data

    def to_internal_value(self, data):
        options = []
        if not isinstance(data, list):
            raise ValidationError(
                "Incorrect type of options. Expected a list."
                f" Got {type(data).__name__}.")

        for item in data:
            if not isinstance(item['id'], six.integer_types):
                raise ValidationError(
                    "Incorrect id type of Option. Expected int. "
                    f"Got {type(item['id']).__name__}.")

            try:
                option = Option.objects.get(pk=item['id'])
            except Option.DoesNotExist:
                raise ValidationError("Option matching query does not exist.")

            options.append(option)
        return {'options': options}


class QuestionSerializer(serializers.ModelSerializer):
    options = OptionField(source='*')

    class Meta:
        model = Question
        fields = ('content', 'options')
        read_only_fields = ('content',)

[attipati kumar]

I thing you don't want to use the save() method. You can always write down for e.g., like this.

class PointSerializer:
    def save(self):
        self.instance = Point(self.validated_data)
        return self.instance

s = PointSerializer(...)
s.is_valid(raise_exception=True)
instance = s.save()

or

You want do instead look like:

my_serializer.is_valid(raise_exception=True)
instance = my_serializer.save()
And also you have a guide with this link's, can you follow it.
1)  http://www.django-rest-framework.org/api-guide/fields/#custom-fields
2)  https://github.com/encode/django-rest-framework/blob/90ed2c1ef7c652ce0a98075c422d25a632d62507/rest_framework/serializers.py#L468-L471

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Thanks & Regards

Kumar A