Class CacheKey

lib/sqlalchemy/sql/cache_key.py:415–564

The key used to identify a SQL statement construct in the SQL compilation cache. .. seealso:: :ref:`sql_caching`

class CacheKey(NamedTuple):
    """The key used to identify a SQL statement construct in the
    SQL compilation cache.

    .. seealso::

        :ref:`sql_caching`

    """

    key: Tuple[Any, ...]
    bindparams: Sequence[BindParameter[Any]]
    params: _CoreSingleExecuteParams | None

    # can't set __hash__ attribute because it interferes
    # with namedtuple
    # can't use "if not TYPE_CHECKING" because mypy rejects it
    # inside of a NamedTuple
    def __hash__(self) -> Optional[int]:  # type: ignore
        """CacheKey itself is not hashable - hash the .key portion"""
        return None

    def to_offline_string(
        self,
        statement_cache: MutableMapping[Any, str],
        statement: ClauseElement,
        parameters: _CoreSingleExecuteParams,
    ) -> str:
        """Generate an "offline string" form of this :class:`.CacheKey`

        The "offline string" is basically the string SQL for the
        statement plus a repr of the bound parameter values in series.
        Whereas the :class:`.CacheKey` object is dependent on in-memory
        identities in order to work as a cache key, the "offline" version
        is suitable for a cache that will work for other processes as well.

        The given ``statement_cache`` is a dictionary-like object where the
        string form of the statement itself will be cached.  This dictionary
        should be in a longer lived scope in order to reduce the time spent
        stringifying statements.


        """
        if self.key not in statement_cache:
            statement_cache[self.key] = sql_str = str(statement)
        else:
            sql_str = statement_cache[self.key]

        if not self.bindparams:
            param_tuple = tuple(parameters[key] for key in sorted(parameters))
        else:
            param_tuple = tuple(
                parameters.get(bindparam.key, bindparam.value)
                for bindparam in self.bindparams
            )

        return repr((sql_str, param_tuple))