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PYTHON-4542 Improved sessions API #2335

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PYTHON-4542 Improved sessions API #2335

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ebb1d62
PYTHON-4542 Improved sessions API
aclark4life May 7, 2025
e090035
Make session var private
aclark4life May 8, 2025
de89b23
Add test for nested sessions.
aclark4life May 8, 2025
85add85
Add context manager
aclark4life May 8, 2025
be283e8
Revert "Add context manager"
aclark4life May 8, 2025
89641f5
Fix session test
aclark4life May 8, 2025
657fcc2
Fix nested session test
aclark4life May 8, 2025
8e008ed
Fix nested session test
aclark4life May 8, 2025
0f9e93a
Set token
aclark4life May 8, 2025
3c68a70
Only bind in __enter__
aclark4life May 23, 2025
71eca08
Only set token if bind is True
aclark4life May 23, 2025
55e833f
Fix token
aclark4life May 23, 2025
c36e9df
Fix test
aclark4life Jun 2, 2025
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12 changes: 12 additions & 0 deletions pymongo/asynchronous/client_session.py
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Original file line number Diff line number Diff line change
Expand Up @@ -139,6 +139,7 @@
import time
import uuid
from collections.abc import Mapping as _Mapping
from contextvars import ContextVar
from typing import (
TYPE_CHECKING,
Any,
Expand Down Expand Up @@ -204,6 +205,7 @@ def __init__(
causal_consistency: Optional[bool] = None,
default_transaction_options: Optional[TransactionOptions] = None,
snapshot: Optional[bool] = False,
bind: Optional[bool] = False,
) -> None:
if snapshot:
if causal_consistency:
Expand All @@ -222,6 +224,7 @@ def __init__(
)
self._default_transaction_options = default_transaction_options
self._snapshot = snapshot
self._bind = bind
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We have to bind/unbind the session in ClientSession.__enter__/__exit__. That way the stack of sessions is managed correctly (ie we call _SESSION.reset(token)). Think about how nested cases will work:

session1 = client.start_session(bind=True)
with session1:
    session2 = client.start_session(bind=True)
    with session2:
        coll.find_one() # uses session2
    coll.find_one() # uses session1
coll.find_one() # uses implicit session

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Done in 3c68a70


@property
def causal_consistency(self) -> bool:
Expand Down Expand Up @@ -514,6 +517,7 @@ def __init__(
# Is this an implicitly created session?
self._implicit = implicit
self._transaction = _Transaction(None, client)
self._token = None

async def end_session(self) -> None:
"""Finish this session. If a transaction has started, abort it.
Expand Down Expand Up @@ -545,9 +549,14 @@ def _check_ended(self) -> None:
raise InvalidOperation("Cannot use ended session")

async def __aenter__(self) -> AsyncClientSession:
if self._options._bind:
self._token = _SESSION.set(self)
return self

async def __aexit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
if self._token:
_SESSION.reset(self._token)
self._token = None
await self._end_session(lock=True)

@property
Expand Down Expand Up @@ -1065,6 +1074,9 @@ def __copy__(self) -> NoReturn:
raise TypeError("A AsyncClientSession cannot be copied, create a new session instead")


_SESSION: ContextVar[Optional[AsyncClientSession]] = ContextVar("SESSION", default=None)


class _EmptyServerSession:
__slots__ = "dirty", "started_retryable_write"

Expand Down
7 changes: 7 additions & 0 deletions pymongo/asynchronous/cursor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -136,9 +136,16 @@ def __init__(
self._killed = False
self._session: Optional[AsyncClientSession]

from .client_session import _SESSION

bound_session = _SESSION.get()

if session:
self._session = session
self._explicit_session = True
elif bound_session:
self._session = bound_session
self._explicit_session = True
else:
self._session = None
self._explicit_session = False
Expand Down
2 changes: 2 additions & 0 deletions pymongo/asynchronous/mongo_client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1362,6 +1362,7 @@ def start_session(
causal_consistency: Optional[bool] = None,
default_transaction_options: Optional[client_session.TransactionOptions] = None,
snapshot: Optional[bool] = False,
bind: Optional[bool] = False,
) -> client_session.AsyncClientSession:
"""Start a logical session.

Expand All @@ -1384,6 +1385,7 @@ def start_session(
causal_consistency=causal_consistency,
default_transaction_options=default_transaction_options,
snapshot=snapshot,
bind=bind,
)

def _ensure_session(
Expand Down
12 changes: 12 additions & 0 deletions pymongo/synchronous/client_session.py
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Original file line number Diff line number Diff line change
Expand Up @@ -139,6 +139,7 @@
import time
import uuid
from collections.abc import Mapping as _Mapping
from contextvars import ContextVar
from typing import (
TYPE_CHECKING,
Any,
Expand Down Expand Up @@ -203,6 +204,7 @@ def __init__(
causal_consistency: Optional[bool] = None,
default_transaction_options: Optional[TransactionOptions] = None,
snapshot: Optional[bool] = False,
bind: Optional[bool] = False,
) -> None:
if snapshot:
if causal_consistency:
Expand All @@ -221,6 +223,7 @@ def __init__(
)
self._default_transaction_options = default_transaction_options
self._snapshot = snapshot
self._bind = bind

@property
def causal_consistency(self) -> bool:
Expand Down Expand Up @@ -513,6 +516,7 @@ def __init__(
# Is this an implicitly created session?
self._implicit = implicit
self._transaction = _Transaction(None, client)
self._token = None

def end_session(self) -> None:
"""Finish this session. If a transaction has started, abort it.
Expand Down Expand Up @@ -544,9 +548,14 @@ def _check_ended(self) -> None:
raise InvalidOperation("Cannot use ended session")

def __enter__(self) -> ClientSession:
if self._options._bind:
self._token = _SESSION.set(self)
return self

def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
if self._token:
_SESSION.reset(self._token)
self._token = None
self._end_session(lock=True)

@property
Expand Down Expand Up @@ -1060,6 +1069,9 @@ def __copy__(self) -> NoReturn:
raise TypeError("A ClientSession cannot be copied, create a new session instead")


_SESSION: ContextVar[Optional[ClientSession]] = ContextVar("SESSION", default=None)


class _EmptyServerSession:
__slots__ = "dirty", "started_retryable_write"

Expand Down
7 changes: 7 additions & 0 deletions pymongo/synchronous/cursor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -136,9 +136,16 @@ def __init__(
self._killed = False
self._session: Optional[ClientSession]

from .client_session import _SESSION

bound_session = _SESSION.get()

if session:
self._session = session
self._explicit_session = True
elif bound_session:
self._session = bound_session
self._explicit_session = True
else:
self._session = None
self._explicit_session = False
Expand Down
2 changes: 2 additions & 0 deletions pymongo/synchronous/mongo_client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1360,6 +1360,7 @@ def start_session(
causal_consistency: Optional[bool] = None,
default_transaction_options: Optional[client_session.TransactionOptions] = None,
snapshot: Optional[bool] = False,
bind: Optional[bool] = False,
) -> client_session.ClientSession:
"""Start a logical session.

Expand All @@ -1382,6 +1383,7 @@ def start_session(
causal_consistency=causal_consistency,
default_transaction_options=default_transaction_options,
snapshot=snapshot,
bind=bind,
)

def _ensure_session(self, session: Optional[ClientSession] = None) -> Optional[ClientSession]:
Expand Down
24 changes: 24 additions & 0 deletions test/asynchronous/test_session.py
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Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,30 @@ async def test_cursor_clone(self):
await cursor.close()
await clone.close()

async def test_bind_session(self):
coll = self.client.pymongo_test.collection

# Explicit session via context variable.
async with self.client.start_session(bind=True) as s:
cursor = coll.find()
self.assertTrue(cursor.session is s)

# Nested sessions.

async def get_cursor(collection):
return collection.find()

session1 = self.client.start_session(bind=True)
async with session1:
session2 = self.client.start_session(bind=True)
async with session2:
cursor = await get_cursor(coll) # uses session2
self.assertEqual(cursor.session, session2)
cursor = await get_cursor(coll) # uses session1
self.assertEqual(cursor.session, session1)
cursor = await get_cursor(coll) # uses implicit session
self.assertEqual(cursor.session, None)

async def test_cursor(self):
listener = self.listener
client = self.client
Expand Down
24 changes: 24 additions & 0 deletions test/test_session.py
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Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,30 @@ def test_cursor_clone(self):
cursor.close()
clone.close()

def test_bind_session(self):
coll = self.client.pymongo_test.collection

# Explicit session via context variable.
with self.client.start_session(bind=True) as s:
cursor = coll.find()
self.assertTrue(cursor.session is s)

# Nested sessions.

def get_cursor(collection):
return collection.find()

session1 = self.client.start_session(bind=True)
with session1:
session2 = self.client.start_session(bind=True)
with session2:
cursor = get_cursor(coll) # uses session2
self.assertEqual(cursor.session, session2)
cursor = get_cursor(coll) # uses session1
self.assertEqual(cursor.session, session1)
cursor = get_cursor(coll) # uses implicit session
self.assertEqual(cursor.session, None)

def test_cursor(self):
listener = self.listener
client = self.client
Expand Down
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