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# engine/characteristics.py
# Copyright (C) 2005-2024 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 .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 connection to its default value."""
@abc.abstractmethod
def set_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
) -> None:
"""set characteristic on the connection to a given value."""
@abc.abstractmethod
def get_characteristic(
self, dialect: Dialect, dbapi_conn: DBAPIConnection
) -> Any:
"""Given a DBAPI connection, get the current value of the
characteristic.
"""
class IsolationLevelCharacteristic(ConnectionCharacteristic):
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)
|
