app/database/base.py

from contextlib import asynccontextmanager
from .models import async_session

@asynccontextmanager
async def get_session():
    """Provide a transactional scope around a series of operations."""
    session = async_session()
    try:
        yield session
        await session.commit()
    except Exception:
        await session.rollback()
        raise
    finally:
        await session.close()