code: def ids(self):
          
          if self._ids is None:
              if self._columns:
                  if isinstance(self._columns, OrderedDict):
                      return [list(self._columns.keys())[0]]
                  return [self._columns[0]]
          else:
              return self._ids
docs: A list of unique IDs used to identify a row.
  
          If not explicitly set, it defaults to the first column name.