class ContentTypeField serializers CharField def to_internal_value sel

class ContentTypeField(serializers.CharField):
    def to_internal_value(self, data):
        if not data:
            return data
        app_label, model = data.split('.')
        return ContentType.objects.get_by_natural_key(app_label, model)

    def to_representation(self, value):
        if not value:
            return value
        return ".".join(value.natural_key())