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python.missing_transaction_boundary

Correctness High

Detects database operations that span multiple queries without proper transaction boundaries, risking partial updates and data inconsistency.

Why It Matters

Without transaction boundaries:

Partial updates — Some changes commit while others fail
Data inconsistency — Database left in invalid state
Race conditions — Concurrent requests see intermediate states
Hard to recover — Manual intervention needed to fix data

Example

# ❌ Before (no transaction boundary)
async def transfer_funds(from_account: str, to_account: str, amount: float):
    await db.execute(
        "UPDATE accounts SET balance = balance - ? WHERE id = ?",
        [amount, from_account]
    )
    # If this fails, money is lost!
    await db.execute(
        "UPDATE accounts SET balance = balance + ? WHERE id = ?",
        [amount, to_account]
    )

# ✅ After (with transaction)
async def transfer_funds(from_account: str, to_account: str, amount: float):
    async with db.transaction():
        await db.execute(
            "UPDATE accounts SET balance = balance - ? WHERE id = ?",
            [amount, from_account]
        )
        await db.execute(
            "UPDATE accounts SET balance = balance + ? WHERE id = ?",
            [amount, to_account]
        )

What Unfault Detects

Multiple database writes without transaction wrapper
Mixed read/write operations without isolation
SQLAlchemy sessions without commit/rollback boundaries
Async database operations without transaction context

Auto-Fix

Unfault generates patches that wrap operations in transactions:

# SQLAlchemy
from sqlalchemy.orm import Session

def create_order(session: Session, order_data: dict):
    with session.begin():
        order = Order(**order_data)
        session.add(order)
        for item in order_data['items']:
            session.add(OrderItem(order=order, **item))

SQLAlchemy Patterns

# Recommended: Use session context manager
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(bind=engine)

def process_data():
    with Session() as session:
        with session.begin():
            # All operations here are in one transaction
            pass
        # Auto-commit on success, rollback on exception