Add database transaction support with atomic operations

- Create transaction.py with @transactional decorator, atomic() context manager
- Add TransactionPropagation modes: REQUIRED, REQUIRES_NEW, NESTED
- Add savepoint support for nested transactions with partial rollback
- Update connection.py with TransactionManager, get_transactional_session
- Update service.py with bulk operations (bulk_mark_downloaded, bulk_delete)
- Wrap QueueRepository.save_item() and clear_all() in atomic transactions
- Add comprehensive tests (66 transaction tests, 90% coverage)
- All 1090 tests passing
This commit is contained in:
2025-12-25 18:05:33 +01:00
parent b2728a7cf4
commit 1ba67357dc
15 changed files with 3385 additions and 202 deletions

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"""Transaction management utilities for SQLAlchemy.
This module provides transaction management utilities including decorators,
context managers, and helper functions for ensuring data consistency
across database operations.
Components:
- @transactional decorator: Wraps functions in transaction boundaries
- TransactionContext: Sync context manager for explicit transaction control
- atomic(): Async context manager for async operations
- TransactionPropagation: Enum for transaction propagation modes
Usage:
@transactional
async def compound_operation(session: AsyncSession, data: Model) -> Result:
# Multiple write operations here
# All succeed or all fail
pass
async with atomic(session) as tx:
# Operations here
async with tx.savepoint() as sp:
# Nested operations with partial rollback capability
pass
"""
from __future__ import annotations
import functools
import logging
from contextlib import asynccontextmanager, contextmanager
from enum import Enum
from typing import (
Any,
AsyncGenerator,
Callable,
Generator,
Optional,
ParamSpec,
TypeVar,
)
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import Session
logger = logging.getLogger(__name__)
# Type variables for generic typing
T = TypeVar("T")
P = ParamSpec("P")
class TransactionPropagation(Enum):
"""Transaction propagation behavior options.
Defines how transactions should behave when called within
an existing transaction context.
Values:
REQUIRED: Use existing transaction or create new one (default)
REQUIRES_NEW: Always create a new transaction (suspend existing)
NESTED: Create a savepoint within existing transaction
"""
REQUIRED = "required"
REQUIRES_NEW = "requires_new"
NESTED = "nested"
class TransactionError(Exception):
"""Exception raised for transaction-related errors."""
class TransactionContext:
"""Synchronous context manager for explicit transaction control.
Provides a clean interface for managing database transactions with
automatic commit/rollback semantics and savepoint support.
Attributes:
session: SQLAlchemy Session instance
_savepoint_count: Counter for nested savepoints
Example:
with TransactionContext(session) as tx:
# Database operations here
with tx.savepoint() as sp:
# Nested operations with partial rollback
pass
"""
def __init__(self, session: Session) -> None:
"""Initialize transaction context.
Args:
session: SQLAlchemy sync session
"""
self.session = session
self._savepoint_count = 0
self._committed = False
def __enter__(self) -> "TransactionContext":
"""Enter transaction context.
Begins a new transaction if not already in one.
Returns:
Self for context manager protocol
"""
logger.debug("Entering transaction context")
# Check if session is already in a transaction
if not self.session.in_transaction():
self.session.begin()
logger.debug("Started new transaction")
return self
def __exit__(
self,
exc_type: Optional[type],
exc_val: Optional[BaseException],
exc_tb: Optional[Any],
) -> bool:
"""Exit transaction context.
Commits on success, rolls back on exception.
Args:
exc_type: Exception type if raised
exc_val: Exception value if raised
exc_tb: Exception traceback if raised
Returns:
False to propagate exceptions
"""
if exc_type is not None:
logger.warning(
"Transaction rollback due to exception: %s: %s",
exc_type.__name__,
exc_val,
)
self.session.rollback()
return False
if not self._committed:
self.session.commit()
logger.debug("Transaction committed")
self._committed = True
return False
@contextmanager
def savepoint(self, name: Optional[str] = None) -> Generator["SavepointContext", None, None]:
"""Create a savepoint for partial rollback capability.
Savepoints allow nested transactions where inner operations
can be rolled back without affecting outer operations.
Args:
name: Optional savepoint name (auto-generated if not provided)
Yields:
SavepointContext for nested transaction control
Example:
with tx.savepoint() as sp:
# Operations here can be rolled back independently
if error_condition:
sp.rollback()
"""
self._savepoint_count += 1
savepoint_name = name or f"sp_{self._savepoint_count}"
logger.debug("Creating savepoint: %s", savepoint_name)
nested = self.session.begin_nested()
sp_context = SavepointContext(nested, savepoint_name)
try:
yield sp_context
if not sp_context._rolled_back:
# Commit the savepoint (release it)
logger.debug("Releasing savepoint: %s", savepoint_name)
except Exception as e:
if not sp_context._rolled_back:
logger.warning(
"Rolling back savepoint %s due to exception: %s",
savepoint_name,
e,
)
nested.rollback()
raise
def commit(self) -> None:
"""Explicitly commit the transaction.
Use this for early commit within the context.
"""
if not self._committed:
self.session.commit()
self._committed = True
logger.debug("Transaction explicitly committed")
def rollback(self) -> None:
"""Explicitly rollback the transaction.
Use this for early rollback within the context.
"""
self.session.rollback()
self._committed = True # Prevent double commit
logger.debug("Transaction explicitly rolled back")
class SavepointContext:
"""Context for managing a database savepoint.
Provides explicit control over savepoint commit/rollback.
Attributes:
_nested: SQLAlchemy nested transaction object
_name: Savepoint name for logging
_rolled_back: Whether rollback has been called
"""
def __init__(self, nested: Any, name: str) -> None:
"""Initialize savepoint context.
Args:
nested: SQLAlchemy nested transaction
name: Savepoint name for logging
"""
self._nested = nested
self._name = name
self._rolled_back = False
def rollback(self) -> None:
"""Rollback to this savepoint.
Undoes all changes since the savepoint was created.
"""
if not self._rolled_back:
self._nested.rollback()
self._rolled_back = True
logger.debug("Savepoint %s rolled back", self._name)
def commit(self) -> None:
"""Commit (release) this savepoint.
Makes changes since the savepoint permanent within
the parent transaction.
"""
if not self._rolled_back:
# SQLAlchemy commits nested transactions automatically
# when exiting the context without rollback
logger.debug("Savepoint %s committed", self._name)
class AsyncTransactionContext:
"""Asynchronous context manager for explicit transaction control.
Provides async interface for managing database transactions with
automatic commit/rollback semantics and savepoint support.
Attributes:
session: SQLAlchemy AsyncSession instance
_savepoint_count: Counter for nested savepoints
Example:
async with AsyncTransactionContext(session) as tx:
# Database operations here
async with tx.savepoint() as sp:
# Nested operations with partial rollback
pass
"""
def __init__(self, session: AsyncSession) -> None:
"""Initialize async transaction context.
Args:
session: SQLAlchemy async session
"""
self.session = session
self._savepoint_count = 0
self._committed = False
async def __aenter__(self) -> "AsyncTransactionContext":
"""Enter async transaction context.
Begins a new transaction if not already in one.
Returns:
Self for context manager protocol
"""
logger.debug("Entering async transaction context")
# Check if session is already in a transaction
if not self.session.in_transaction():
await self.session.begin()
logger.debug("Started new async transaction")
return self
async def __aexit__(
self,
exc_type: Optional[type],
exc_val: Optional[BaseException],
exc_tb: Optional[Any],
) -> bool:
"""Exit async transaction context.
Commits on success, rolls back on exception.
Args:
exc_type: Exception type if raised
exc_val: Exception value if raised
exc_tb: Exception traceback if raised
Returns:
False to propagate exceptions
"""
if exc_type is not None:
logger.warning(
"Async transaction rollback due to exception: %s: %s",
exc_type.__name__,
exc_val,
)
await self.session.rollback()
return False
if not self._committed:
await self.session.commit()
logger.debug("Async transaction committed")
self._committed = True
return False
@asynccontextmanager
async def savepoint(
self, name: Optional[str] = None
) -> AsyncGenerator["AsyncSavepointContext", None]:
"""Create an async savepoint for partial rollback capability.
Args:
name: Optional savepoint name (auto-generated if not provided)
Yields:
AsyncSavepointContext for nested transaction control
"""
self._savepoint_count += 1
savepoint_name = name or f"sp_{self._savepoint_count}"
logger.debug("Creating async savepoint: %s", savepoint_name)
nested = await self.session.begin_nested()
sp_context = AsyncSavepointContext(nested, savepoint_name, self.session)
try:
yield sp_context
if not sp_context._rolled_back:
logger.debug("Releasing async savepoint: %s", savepoint_name)
except Exception as e:
if not sp_context._rolled_back:
logger.warning(
"Rolling back async savepoint %s due to exception: %s",
savepoint_name,
e,
)
await nested.rollback()
raise
async def commit(self) -> None:
"""Explicitly commit the async transaction."""
if not self._committed:
await self.session.commit()
self._committed = True
logger.debug("Async transaction explicitly committed")
async def rollback(self) -> None:
"""Explicitly rollback the async transaction."""
await self.session.rollback()
self._committed = True # Prevent double commit
logger.debug("Async transaction explicitly rolled back")
class AsyncSavepointContext:
"""Async context for managing a database savepoint.
Attributes:
_nested: SQLAlchemy nested transaction object
_name: Savepoint name for logging
_session: Parent session for async operations
_rolled_back: Whether rollback has been called
"""
def __init__(
self, nested: Any, name: str, session: AsyncSession
) -> None:
"""Initialize async savepoint context.
Args:
nested: SQLAlchemy nested transaction
name: Savepoint name for logging
session: Parent async session
"""
self._nested = nested
self._name = name
self._session = session
self._rolled_back = False
async def rollback(self) -> None:
"""Rollback to this savepoint asynchronously."""
if not self._rolled_back:
await self._nested.rollback()
self._rolled_back = True
logger.debug("Async savepoint %s rolled back", self._name)
async def commit(self) -> None:
"""Commit (release) this savepoint asynchronously."""
if not self._rolled_back:
logger.debug("Async savepoint %s committed", self._name)
@asynccontextmanager
async def atomic(
session: AsyncSession,
propagation: TransactionPropagation = TransactionPropagation.REQUIRED,
) -> AsyncGenerator[AsyncTransactionContext, None]:
"""Async context manager for atomic database operations.
Provides a clean interface for wrapping database operations in
a transaction boundary with automatic commit/rollback.
Args:
session: SQLAlchemy async session
propagation: Transaction propagation behavior
Yields:
AsyncTransactionContext for transaction control
Example:
async with atomic(session) as tx:
await some_operation(session)
await another_operation(session)
# All operations committed together or rolled back
async with atomic(session) as tx:
await outer_operation(session)
async with tx.savepoint() as sp:
await risky_operation(session)
if error:
await sp.rollback() # Only rollback nested ops
"""
logger.debug(
"Starting atomic block with propagation: %s",
propagation.value,
)
if propagation == TransactionPropagation.NESTED:
# Use savepoint for nested propagation
if session.in_transaction():
nested = await session.begin_nested()
sp_context = AsyncSavepointContext(nested, "atomic_nested", session)
try:
# Create a wrapper context for consistency
wrapper = AsyncTransactionContext(session)
wrapper._committed = True # Parent manages commit
yield wrapper
if not sp_context._rolled_back:
logger.debug("Releasing nested atomic savepoint")
except Exception as e:
if not sp_context._rolled_back:
logger.warning(
"Rolling back nested atomic savepoint due to: %s", e
)
await nested.rollback()
raise
else:
# No existing transaction, start new one
async with AsyncTransactionContext(session) as tx:
yield tx
else:
# REQUIRED or REQUIRES_NEW
async with AsyncTransactionContext(session) as tx:
yield tx
@contextmanager
def atomic_sync(
session: Session,
propagation: TransactionPropagation = TransactionPropagation.REQUIRED,
) -> Generator[TransactionContext, None, None]:
"""Sync context manager for atomic database operations.
Args:
session: SQLAlchemy sync session
propagation: Transaction propagation behavior
Yields:
TransactionContext for transaction control
"""
logger.debug(
"Starting sync atomic block with propagation: %s",
propagation.value,
)
if propagation == TransactionPropagation.NESTED:
if session.in_transaction():
nested = session.begin_nested()
sp_context = SavepointContext(nested, "atomic_nested")
try:
wrapper = TransactionContext(session)
wrapper._committed = True
yield wrapper
if not sp_context._rolled_back:
logger.debug("Releasing nested sync atomic savepoint")
except Exception as e:
if not sp_context._rolled_back:
logger.warning(
"Rolling back nested sync savepoint due to: %s", e
)
nested.rollback()
raise
else:
with TransactionContext(session) as tx:
yield tx
else:
with TransactionContext(session) as tx:
yield tx
def transactional(
propagation: TransactionPropagation = TransactionPropagation.REQUIRED,
session_param: str = "db",
) -> Callable[[Callable[P, T]], Callable[P, T]]:
"""Decorator to wrap a function in a transaction boundary.
Automatically handles commit on success and rollback on exception.
Works with both sync and async functions.
Args:
propagation: Transaction propagation behavior
session_param: Name of the session parameter in the function signature
Returns:
Decorated function wrapped in transaction
Example:
@transactional()
async def create_user_with_profile(db: AsyncSession, data: dict):
user = await create_user(db, data['user'])
profile = await create_profile(db, user.id, data['profile'])
return user, profile
@transactional(propagation=TransactionPropagation.NESTED)
async def risky_sub_operation(db: AsyncSession, data: dict):
# This can be rolled back without affecting parent transaction
pass
"""
def decorator(func: Callable[P, T]) -> Callable[P, T]:
import asyncio
if asyncio.iscoroutinefunction(func):
@functools.wraps(func)
async def async_wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
# Get session from kwargs or args
session = _extract_session(func, args, kwargs, session_param)
if session is None:
raise TransactionError(
f"Could not find session parameter '{session_param}' "
f"in function {func.__name__}"
)
logger.debug(
"Starting transaction for %s with propagation %s",
func.__name__,
propagation.value,
)
async with atomic(session, propagation):
result = await func(*args, **kwargs)
logger.debug(
"Transaction completed for %s",
func.__name__,
)
return result
return async_wrapper # type: ignore
else:
@functools.wraps(func)
def sync_wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
# Get session from kwargs or args
session = _extract_session(func, args, kwargs, session_param)
if session is None:
raise TransactionError(
f"Could not find session parameter '{session_param}' "
f"in function {func.__name__}"
)
logger.debug(
"Starting sync transaction for %s with propagation %s",
func.__name__,
propagation.value,
)
with atomic_sync(session, propagation):
result = func(*args, **kwargs)
logger.debug(
"Sync transaction completed for %s",
func.__name__,
)
return result
return sync_wrapper # type: ignore
return decorator
def _extract_session(
func: Callable,
args: tuple,
kwargs: dict,
session_param: str,
) -> Optional[AsyncSession | Session]:
"""Extract session from function arguments.
Args:
func: The function being called
args: Positional arguments
kwargs: Keyword arguments
session_param: Name of the session parameter
Returns:
Session instance or None if not found
"""
import inspect
# Check kwargs first
if session_param in kwargs:
return kwargs[session_param]
# Get function signature to find positional index
sig = inspect.signature(func)
params = list(sig.parameters.keys())
if session_param in params:
idx = params.index(session_param)
# Account for 'self' parameter in methods
if len(args) > idx:
return args[idx]
return None
def is_in_transaction(session: AsyncSession | Session) -> bool:
"""Check if session is currently in a transaction.
Args:
session: SQLAlchemy session (sync or async)
Returns:
True if session is in an active transaction
"""
return session.in_transaction()
def get_transaction_depth(session: AsyncSession | Session) -> int:
"""Get the current transaction nesting depth.
Args:
session: SQLAlchemy session (sync or async)
Returns:
Number of nested transactions (0 if not in transaction)
"""
# SQLAlchemy doesn't expose nesting depth directly,
# but we can check transaction state
if not session.in_transaction():
return 0
# Check for nested transaction
if hasattr(session, '_nested_transaction') and session._nested_transaction:
return 2 # At least one savepoint
return 1
__all__ = [
"TransactionPropagation",
"TransactionError",
"TransactionContext",
"AsyncTransactionContext",
"SavepointContext",
"AsyncSavepointContext",
"atomic",
"atomic_sync",
"transactional",
"is_in_transaction",
"get_transaction_depth",
]