# engine/characteristics.py
# Copyright (C) 2005-2025 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
from __future__ import annotations
import abc
import typing
from typing import Any
from typing import ClassVar
if typing.TYPE_CHECKING:
from .base import Connection
from .interfaces import DBAPIConnection
from .interfaces import Dialect
class ConnectionCharacteristic(abc.ABC):
"""An abstract base for an object that can set, get and reset a
per-connection characteristic, typically one that gets reset when the
connection is returned to the connection pool.
transaction isolation is the canonical example, and the
``IsolationLevelCharacteristic`` implementation provides this for the
``DefaultDialect``.
The ``ConnectionCharacteristic`` class should call upon the ``Dialect`` for
the implementation of each method. The object exists strictly to serve as
a dialect visitor that can be placed into the
``DefaultDialect.connection_characteristics`` dictionary where it will take
effect for calls to :meth:`_engine.Connection.execution_options` and
related APIs.
.. versionadded:: 1.4
"""
__slots__ = ()
transactional: ClassVar[bool] = False
@abc.abstractmethod
def reset_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> None:
"""Reset the characteristic on the DBAPI connection to its default
value."""
@abc.abstractmethod
def set_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
) -> None:
"""set characteristic on the DBAPI connection to a given value."""
def set_connection_characteristic(
self,
dialect: Dialect,
conn: Connection,
dbapi_conn: DBAPIConnection,
value: Any,
) -> None:
"""set characteristic on the :class:`_engine.Connection` to a given
value.
.. versionadded:: 2.0.30 - added to support elements that are local
to the :class:`_engine.Connection` itself.
"""
self.set_characteristic(dialect, dbapi_conn, value)
@abc.abstractmethod
def get_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> Any:
"""Given a DBAPI connection, get the current value of the
characteristic.
"""
def get_connection_characteristic(
self, dialect: Dialect, conn: Connection, dbapi_conn: DBAPIConnection
) -> Any:
"""Given a :class:`_engine.Connection`, get the current value of the
characteristic.
.. versionadded:: 2.0.30 - added to support elements that are local
to the :class:`_engine.Connection` itself.
"""
return self.get_characteristic(dialect, dbapi_conn)
class IsolationLevelCharacteristic(ConnectionCharacteristic):
"""Manage the isolation level on a DBAPI connection"""
transactional: ClassVar[bool] = True
def reset_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> None:
dialect.reset_isolation_level(dbapi_conn)
def set_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
) -> None:
dialect._assert_and_set_isolation_level(dbapi_conn, value)
def get_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> Any:
return dialect.get_isolation_level(dbapi_conn)
class LoggingTokenCharacteristic(ConnectionCharacteristic):
"""Manage the 'logging_token' option of a :class:`_engine.Connection`.
.. versionadded:: 2.0.30
"""
transactional: ClassVar[bool] = False
def reset_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> None:
pass
def set_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
) -> None:
raise NotImplementedError()
def set_connection_characteristic(
self,
dialect: Dialect,
conn: Connection,
dbapi_conn: DBAPIConnection,
value: Any,
) -> None:
if value:
conn._message_formatter = lambda msg: "[%s] %s" % (value, msg)
else:
del conn._message_formatter
def get_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> Any:
raise NotImplementedError()
def get_connection_characteristic(
self, dialect: Dialect, conn: Connection, dbapi_conn: DBAPIConnection
) -> Any:
return conn._execution_options.get("logging_token", None)
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