def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def add_backend(self, backend):
        """
        Adds a new backend to the list

        @param backend_id: the id of the backend to add
        """
        if backend:
            backend_iter = self.liststore.append([
                backend.get_id(),
                self.dialog.get_pixbuf_from_icon_name(backend.get_icon(),
                                                      16),
                backend.get_human_name(),
                self._get_markup_for_tags(backend.get_attached_tags()),
            ])
            self.backendid_to_iter[backend.get_id()] = backend_iter