The ManyToMany field on the item class pointing to this class.

        If there is more than one field, this value will be None.

def item_related_name(self):
        """
        The ManyToMany field on the item class pointing to this class.

        If there is more than one field, this value will be None.
        """
        if not hasattr(self, '_item_related_name'):
            many_to_many_rels = \
                get_section_many_to_many_relations(self.__class__)
            if len(many_to_many_rels) != 1:
                self._item_related_name = None
            else:
                self._item_related_name = many_to_many_rels[0].field.name
        return self._item_related_name