class Serializer

    def field_from_native(self, data, files, field_name, into):
        """
        Override default so that the serializer can be used as a writable
        nested field across relationships.
        """
        if self.read_only:
            return

        try:
            value = data[field_name]
        except KeyError:
            if self.default is not None and not self.partial:
                # Note: partial updates shouldn't set defaults
                value = copy.deepcopy(self.default)
            else:
                if self.required:
                    raise ValidationError(self.error_messages['required'])
                return

        if self.source == '*':
            if value:
                reverted_data = self.restore_fields(value, {})
                if not self._errors:
                    into.update(reverted_data)
        else:
            if value in (None, ''):
                into[(self.source or field_name)] = None
            else:
                # Set the serializer object if it exists
                obj = get_component(self.parent.object, self.source or field_name) if self.parent.object else None

                # If we have a model manager or similar object then we need
                # to iterate through each instance.
                if (self.many and
                    not hasattr(obj, '__iter__') and
                    is_simple_callable(getattr(obj, 'all', None))):
                    obj = obj.all()

                kwargs = {
                    'instance': obj,
                    'data': value,
                    'context': self.context,
                    'partial': self.partial,
                    'many': self.many,
                    'allow_add_remove': self.allow_add_remove
                }
                serializer = self.__class__(**kwargs)

                if serializer.is_valid():
                    into[self.source or field_name] = serializer.object
                else:
                    # Propagate errors up to our parent
                    raise NestedValidationError(serializer.errors)

    def field_from_native(self, data, files, field_name, into):
        """
        Given a dictionary and a field name, updates the dictionary `into`,
        with the field and it's deserialized value.
        """
        if self.read_only:
            return

        try:
            data = data or {}
            if self.use_files:
                files = files or {}
                try:
                    native = files[field_name]
                except KeyError:
                    native = data[field_name]
            else:
                native = data[field_name]
        except KeyError:
            if self.default is not None and not self.partial:
                # Note: partial updates shouldn't set defaults
                native = self.get_default_value()
            else:
                if self.required:
                    raise ValidationError(self.error_messages['required'])
                return

        value = self.from_native(native)
        if self.source == '*':
            if value:
                into.update(value)
        else:
            self.validate(value)
            self.run_validators(value)
            into[self.source or field_name] = value

    def field_from_native(self, data, files, field_name, into):
        """
        Given a dictionary and a field name, updates the dictionary `into`,
        with the field and it's deserialized value.
        """
        return

    def field_to_native(self, obj, field_name):
        """
        Override default so that the serializer can be used as a nested field
        across relationships.
        """
        if self.write_only:
            return None

        if self.source == '*':
            return self.to_native(obj)

        # Get the raw field value
        try:
            source = self.source or field_name
            value = obj

            for component in source.split('.'):
                if value is None:
                    break
                value = get_component(value, component)
        except ObjectDoesNotExist:
            return None

        if is_simple_callable(getattr(value, 'all', None)):
            return [self.to_native(item) for item in value.all()]

        if value is None:
            return None

        if self.many is not None:
            many = self.many
        else:
            many = hasattr(value, '__iter__') and not isinstance(value, (Page, dict, six.text_type))

        if many:
            return [self.to_native(item) for item in value]
        return self.to_native(value)

    def field_to_native(self, obj, field_name):
        if self.write_only:
            return None
        return super(WritableField, self).field_to_native(obj, field_name)

    def field_to_native(self, obj, field_name):
        """
        Given and object and a field name, returns the value that should be
        serialized for that field.
        """
        if obj is None:
            return self.empty

        if self.source == '*':
            return self.to_native(obj)

        source = self.source or field_name
        value = obj

        for component in source.split('.'):
            value = get_component(value, component)
            if value is None:
                break

        return self.to_native(value)

    def from_native(self, data, files=None):
        """
        Deserialize primitives -> objects.
        """
        self._errors = {}

        if data is not None or files is not None:
            attrs = self.restore_fields(data, files)
            if attrs is not None:
                attrs = self.perform_validation(attrs)
        else:
            self._errors['non_field_errors'] = ['No input provided']

        if not self._errors:
            return self.restore_object(attrs, instance=getattr(self, 'object', None))

    def from_native(self, value):
        """
        Reverts a simple representation back to the field's value.
        """
        return value

    def metadata(self):
        """
        Return a dictionary of metadata about the fields on the serializer.
        Useful for things like responding to OPTIONS requests, or generating
        API schemas for auto-documentation.
        """
        return SortedDict(
            [(field_name, field.metadata())
            for field_name, field in six.iteritems(self.fields)]
        )

    def metadata(self):
        metadata = SortedDict()
        metadata['type'] = self.type_label
        metadata['required'] = getattr(self, 'required', False)
        optional_attrs = ['read_only', 'label', 'help_text',
                          'min_length', 'max_length']
        for attr in optional_attrs:
            value = getattr(self, attr, None)
            if value is not None and value != '':
                metadata[attr] = force_text(value, strings_only=True)
        return metadata

    def to_native(self, obj):
        """
        Serialize objects -> primitives.
        """
        ret = self._dict_class()
        ret.fields = self._dict_class()

        for field_name, field in self.fields.items():
            if field.read_only and obj is None:
                continue
            field.initialize(parent=self, field_name=field_name)
            key = self.get_field_key(field_name)
            value = field.field_to_native(obj, field_name)
            method = getattr(self, 'transform_%s' % field_name, None)
            if callable(method):
                value = method(obj, value)
            if not getattr(field, 'write_only', False):
                ret[key] = value
            ret.fields[key] = self.augment_field(field, field_name, key, value)

        return ret

    def to_native(self, value):
        """
        Converts the field's value into it's simple representation.
        """
        if is_simple_callable(value):
            value = value()

        if is_protected_type(value):
            return value
        elif (is_non_str_iterable(value) and
              not isinstance(value, (dict, six.string_types))):
            return [self.to_native(item) for item in value]
        elif isinstance(value, dict):
            # Make sure we preserve field ordering, if it exists
            ret = SortedDict()
            for key, val in value.items():
                ret[key] = self.to_native(val)
            return ret
        return force_text(value)

    def validate(self, attrs):
        """
        Stub method, to be overridden in Serializer subclasses
        """
        return attrs

    def validate(self, value):
        if value in validators.EMPTY_VALUES and self.required:
            raise ValidationError(self.error_messages['required'])