code: def _rpc_metadata(self):
          
          if self._rpc_metadata_internal is None:
              self._rpc_metadata_internal = _helpers.metadata_with_prefix(
                  self._database_string
              )
  
          return self._rpc_metadata_internal
docs: The RPC metadata for this client's associated database.
  
          Returns:
              Sequence[Tuple(str, str)]: RPC metadata with resource prefix
              for the database associated with this client.