              msg = self.error_messages['invalid']
              raise ValidationError(msg)
  
  
  class ManySlugRelatedField(ManyRelatedMixin, SlugRelatedField):
      form_field_class = forms.MultipleChoiceField
  
  
  ### Hyperlinked relationships
  
  class HyperlinkedRelatedField(RelatedField):
      """
      Represents a to-one relationship, using hyperlinking.
 
</s> remove class ManyHyperlinkedRelatedField(ManyRelatedMixin, HyperlinkedRelatedField):
    """
    Represents a to-many relationship, using hyperlinking.
    """
    form_field_class = forms.MultipleChoiceField


 </s> add  </s> remove class ManyRelatedMixin(object):
    """
    Mixin to convert a related field to a many related field.
    """
    widget = widgets.SelectMultiple

    def field_to_native(self, obj, field_name):
        value = getattr(obj, self.source or field_name)
        return [self.to_native(item) for item in value.all()]

    def field_from_native(self, data, files, field_name, into):
        if self.read_only:
            return

        try:
            # Form data
            value = data.getlist(self.source or field_name)
        except:
            # Non-form data
            value = data.get(self.source or field_name)
        else:
            if value == ['']:
                value = []

        into[field_name] = [self.from_native(item) for item in value]


class ManyRelatedField(ManyRelatedMixin, RelatedField):
    """
    Base class for related model managers.

    If not overridden, this represents a to-many relationship, using the unicode
    representations of the target, and is read-only.
    """
    pass


 </s> add  </s> remove         data = {'rel': ''}
 </s> add         data = MultiValueDict()
        data.setlist('rel', ['']) </s> remove             value = data[field_name]
 </s> add             if self.many:
                try:
                    # Form data
                    value = data.getlist(field_name)
                    if value == ['']:
                        value = []
                except AttributeError:
                    # Non-form data
                    value = data[field_name]
            else:
                value = data[field_name]
              msg = self.error_messages['invalid']
              raise ValidationError(msg)
  
  




  ### Hyperlinked relationships
  
  class HyperlinkedRelatedField(RelatedField):
      """
      Represents a to-one relationship, using hyperlinking.
keep keep keep keep replace replace replace replace keep keep keep keep keep
 Starting migration from ManyField to Field(many=True) 
rest_framework/relations.py