# pool/events.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 typing
from typing import Any
from typing import Optional
from typing import Type
from typing import Union
from .base import ConnectionPoolEntry
from .base import Pool
from .base import PoolProxiedConnection
from .base import PoolResetState
from .. import event
from .. import util
if typing.TYPE_CHECKING:
from ..engine import Engine
from ..engine.interfaces import DBAPIConnection
class PoolEvents(event.Events[Pool]):
"""Available events for :class:`_pool.Pool`.
The methods here define the name of an event as well
as the names of members that are passed to listener
functions.
e.g.::
from sqlalchemy import event
def my_on_checkout(dbapi_conn, connection_rec, connection_proxy):
"handle an on checkout event"
event.listen(Pool, "checkout", my_on_checkout)
In addition to accepting the :class:`_pool.Pool` class and
:class:`_pool.Pool` instances, :class:`_events.PoolEvents` also accepts
:class:`_engine.Engine` objects and the :class:`_engine.Engine` class as
targets, which will be resolved to the ``.pool`` attribute of the
given engine or the :class:`_pool.Pool` class::
engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test")
# will associate with engine.pool
event.listen(engine, "checkout", my_on_checkout)
""" # noqa: E501
_target_class_doc = "SomeEngineOrPool"
_dispatch_target = Pool
@util.preload_module("sqlalchemy.engine")
@classmethod
def _accept_with(
cls,
target: Union[Pool, Type[Pool], Engine, Type[Engine]],
identifier: str,
) -> Optional[Union[Pool, Type[Pool]]]:
if not typing.TYPE_CHECKING:
Engine = util.preloaded.engine.Engine
if isinstance(target, type):
if issubclass(target, Engine):
return Pool
else:
assert issubclass(target, Pool)
return target
elif isinstance(target, Engine):
return target.pool
elif isinstance(target, Pool):
return target
elif hasattr(target, "_no_async_engine_events"):
target._no_async_engine_events()
else:
return None
@classmethod
def _listen(
cls,
event_key: event._EventKey[Pool],
**kw: Any,
) -> None:
target = event_key.dispatch_target
kw.setdefault("asyncio", target._is_asyncio)
event_key.base_listen(**kw)
def connect(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
) -> None:
"""Called at the moment a particular DBAPI connection is first
created for a given :class:`_pool.Pool`.
This event allows one to capture the point directly after which
the DBAPI module-level ``.connect()`` method has been used in order
to produce a new DBAPI connection.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
"""
def first_connect(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
) -> None:
"""Called exactly once for the first time a DBAPI connection is
checked out from a particular :class:`_pool.Pool`.
The rationale for :meth:`_events.PoolEvents.first_connect`
is to determine
information about a particular series of database connections based
on the settings used for all connections. Since a particular
:class:`_pool.Pool`
refers to a single "creator" function (which in terms
of a :class:`_engine.Engine`
refers to the URL and connection options used),
it is typically valid to make observations about a single connection
that can be safely assumed to be valid about all subsequent
connections, such as the database version, the server and client
encoding settings, collation settings, and many others.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
"""
def checkout(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
connection_proxy: PoolProxiedConnection,
) -> None:
"""Called when a connection is retrieved from the Pool.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
:param connection_proxy: the :class:`.PoolProxiedConnection` object
which will proxy the public interface of the DBAPI connection for the
lifespan of the checkout.
If you raise a :class:`~sqlalchemy.exc.DisconnectionError`, the current
connection will be disposed and a fresh connection retrieved.
Processing of all checkout listeners will abort and restart
using the new connection.
.. seealso:: :meth:`_events.ConnectionEvents.engine_connect`
- a similar event
which occurs upon creation of a new :class:`_engine.Connection`.
"""
def checkin(
self,
dbapi_connection: Optional[DBAPIConnection],
connection_record: ConnectionPoolEntry,
) -> None:
"""Called when a connection returns to the pool.
Note that the connection may be closed, and may be None if the
connection has been invalidated. ``checkin`` will not be called
for detached connections. (They do not return to the pool.)
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
"""
@event._legacy_signature(
"2.0",
["dbapi_connection", "connection_record"],
lambda dbapi_connection, connection_record, reset_state: (
dbapi_connection,
connection_record,
),
)
def reset(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
reset_state: PoolResetState,
) -> None:
"""Called before the "reset" action occurs for a pooled connection.
This event represents
when the ``rollback()`` method is called on the DBAPI connection
before it is returned to the pool or discarded.
A custom "reset" strategy may be implemented using this event hook,
which may also be combined with disabling the default "reset"
behavior using the :paramref:`_pool.Pool.reset_on_return` parameter.
The primary difference between the :meth:`_events.PoolEvents.reset` and
:meth:`_events.PoolEvents.checkin` events are that
:meth:`_events.PoolEvents.reset` is called not just for pooled
connections that are being returned to the pool, but also for
connections that were detached using the
:meth:`_engine.Connection.detach` method as well as asyncio connections
that are being discarded due to garbage collection taking place on
connections before the connection was checked in.
Note that the event **is not** invoked for connections that were
invalidated using :meth:`_engine.Connection.invalidate`. These
events may be intercepted using the :meth:`.PoolEvents.soft_invalidate`
and :meth:`.PoolEvents.invalidate` event hooks, and all "connection
close" events may be intercepted using :meth:`.PoolEvents.close`.
The :meth:`_events.PoolEvents.reset` event is usually followed by the
:meth:`_events.PoolEvents.checkin` event, except in those
cases where the connection is discarded immediately after reset.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
:param reset_state: :class:`.PoolResetState` instance which provides
information about the circumstances under which the connection
is being reset.
.. versionadded:: 2.0
.. seealso::
:ref:`pool_reset_on_return`
:meth:`_events.ConnectionEvents.rollback`
:meth:`_events.ConnectionEvents.commit`
"""
def invalidate(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
exception: Optional[BaseException],
) -> None:
"""Called when a DBAPI connection is to be "invalidated".
This event is called any time the
:meth:`.ConnectionPoolEntry.invalidate` method is invoked, either from
API usage or via "auto-invalidation", without the ``soft`` flag.
The event occurs before a final attempt to call ``.close()`` on the
connection occurs.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
:param exception: the exception object corresponding to the reason
for this invalidation, if any. May be ``None``.
.. seealso::
:ref:`pool_connection_invalidation`
"""
def soft_invalidate(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
exception: Optional[BaseException],
) -> None:
"""Called when a DBAPI connection is to be "soft invalidated".
This event is called any time the
:meth:`.ConnectionPoolEntry.invalidate`
method is invoked with the ``soft`` flag.
Soft invalidation refers to when the connection record that tracks
this connection will force a reconnect after the current connection
is checked in. It does not actively close the dbapi_connection
at the point at which it is called.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
:param exception: the exception object corresponding to the reason
for this invalidation, if any. May be ``None``.
"""
def close(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
) -> None:
"""Called when a DBAPI connection is closed.
The event is emitted before the close occurs.
The close of a connection can fail; typically this is because
the connection is already closed. If the close operation fails,
the connection is discarded.
The :meth:`.close` event corresponds to a connection that's still
associated with the pool. To intercept close events for detached
connections use :meth:`.close_detached`.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
"""
def detach(
self,
dbapi_connection: DBAPIConnection,
connection_record: ConnectionPoolEntry,
) -> None:
"""Called when a DBAPI connection is "detached" from a pool.
This event is emitted after the detach occurs. The connection
is no longer associated with the given connection record.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
:param connection_record: the :class:`.ConnectionPoolEntry` managing
the DBAPI connection.
"""
def close_detached(self, dbapi_connection: DBAPIConnection) -> None:
"""Called when a detached DBAPI connection is closed.
The event is emitted before the close occurs.
The close of a connection can fail; typically this is because
the connection is already closed. If the close operation fails,
the connection is discarded.
:param dbapi_connection: a DBAPI connection.
The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
"""
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