docs: def datafile(self):
          """Return an MPR datafile from the /ingest directory of the build filesystem"""
          from ambry_sources import MPRowsFile
  
          if self._datafile is None:
              if self.urltype == 'partition':
                      self._datafile = self.partition.datafile
              else:
                  self._datafile = MPRowsFile(self._bundle.build_ingest_fs, self.name)
  
          return self._datafile