Class PrimaryPreferred

pymongo/read_preferences.py:308–352

PrimaryPreferred read preference. * When directly connected to one mongod queries are allowed to standalone servers, to a replica set primary, or to replica set secondaries. * When connected to a mongos queries are sent to the primary of a shard if available, otherwise a shard s

class PrimaryPreferred(_ServerMode):
    """PrimaryPreferred read preference.

    * When directly connected to one mongod queries are allowed to standalone
      servers, to a replica set primary, or to replica set secondaries.
    * When connected to a mongos queries are sent to the primary of a shard if
      available, otherwise a shard secondary.
    * When connected to a replica set queries are sent to the primary if
      available, otherwise a secondary.

    .. note:: When a :class:`~pymongo.mongo_client.MongoClient` is first
      created reads will be routed to an available secondary until the
      primary of the replica set is discovered.

    :param tag_sets: The :attr:`~tag_sets` to use if the primary is not
        available.
    :param max_staleness: (integer, in seconds) The maximum estimated
        length of time a replica set secondary can fall behind the primary in
        replication before it will no longer be selected for operations.
        Default -1, meaning no maximum. If it is set, it must be at least
        90 seconds.
    :param hedge: **DEPRECATED** - The :attr:`~hedge` for this read preference.

    .. versionchanged:: 3.11
       Added ``hedge`` parameter.
    """

    __slots__ = ()

    def __init__(
        self,
        tag_sets: Optional[_TagSets] = None,
        max_staleness: int = -1,
        hedge: Optional[_Hedge] = None,
    ) -> None:
        super().__init__(_PRIMARY_PREFERRED, tag_sets, max_staleness, hedge)

    def __call__(self, selection: Selection) -> Selection:
        """Apply this read preference to Selection."""
        if selection.primary:
            return selection.primary_selection
        else:
            return secondary_with_tags_server_selector(
                self.tag_sets, max_staleness_selectors.select(self.max_staleness, selection)
            )


class Secondary(_ServerMode):