👀 Views: 81 💬 Answers: 1 📅 Created: 2025-07-14

fastapi sqlalchemy asyncio Python

I'm converting an old project and I'm migrating some code and I'm working on a FastAPI application where I'm using SQLAlchemy for database interactions. I have a function that is supposed to fetch user data asynchronously, but I'm running into issues where the data returned is sometimes inconsistent or stale. Specifically, I have an endpoint that looks like this: ```python from fastapi import FastAPI, Depends from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine from sqlalchemy.orm import sessionmaker, declarative_base DATABASE_URL = "postgresql+asyncpg://user:password@localhost/db" engine = create_async_engine(DATABASE_URL, echo=True) Base = declarative_base() AsyncSessionLocal = sessionmaker(bind=engine, class_=AsyncSession, expire_on_commit=False) app = FastAPI() class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) name = Column(String) async def get_db(): async with AsyncSessionLocal() as session: yield session @app.get("/users/{user_id}") async def read_user(user_id: int, db: AsyncSession = Depends(get_db)): result = await db.execute(select(User).where(User.id == user_id)) user = result.scalar_one_or_none() return user ``` I've noticed that if a user is updated in the database while I’m fetching their data, I sometimes receive stale information. I tried adding `.refresh(user)` after fetching the user, but I still encounter issues where changes aren’t reflected immediately. The `expire_on_commit` parameter is set to `False`, which I thought would help manage sessions better, but it seems not to be functioning as expected. I also included logging to track the database queries being executed, and they seem correct, but the results often don’t match what's in the database right after an update. I suspect there might be some caching behavior happening that I’m unaware of. Furthermore, I’m using FastAPI 0.75.0 and SQLAlchemy 1.4.25. Any insights on how to handle this properly? Is there something specific I could be missing in managing sessions or the async lifecycle? What am I doing wrong? This is for a service running on macOS. What's the correct way to implement this? Thanks for taking the time to read this! Any suggestions would be helpful.