code: def _read_json_db(self):
          
          try:
              metadata_str = self.db_io.read_metadata_from_uri(
                  self.layer_uri, 'json')
          except HashNotFoundError:
              return {}
          try:
              metadata = json.loads(metadata_str)
              return metadata
          except ValueError:
              message = tr('the file DB entry for %s does not appear to be '
                           'valid JSON')
              message %= self.layer_uri
              raise MetadataReadError(message)
docs: read metadata from a json string stored in a DB.
  
          :return: the parsed json dict
          :rtype: dict