👀 Views: 67 💬 Answers: 1 📅 Created: 2025-06-08

fastapi sqlalchemy asyncio Python

I'm sure I'm missing something obvious here, but I'm currently developing a FastAPI application and trying to implement asynchronous database queries using SQLAlchemy and asyncpg for PostgreSQL... However, I'm working with a `ValueError: A session is required for this operation` behavior when I attempt to execute a query. Here's a snippet of my code: ```python from fastapi import FastAPI, Depends from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker DATABASE_URL = 'postgresql+asyncpg://user:password@localhost/dbname' engine = create_async_engine(DATABASE_URL, echo=True) Base = declarative_base() AsyncSessionLocal = sessionmaker(bind=engine, class_=AsyncSession, expire_on_commit=False) app = FastAPI() 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 made sure to use `async with` for the session context, and I have the latest versions of FastAPI (0.68.0) and SQLAlchemy (1.4.22) installed. Additionally, I've confirmed that my database connection string is correct and the PostgreSQL server is running without issues. Despite all this, I still receive the `ValueError` when trying to fetch a user by ID. Could this be an scenario with how the session is being managed, or is there something else I might be missing in my async setup? Any guidance would be greatly appreciated! I'm working on a CLI tool that needs to handle this. I'd love to hear your thoughts on this. What would be the recommended way to handle this? This issue appeared after updating to Python 3.9. I'd really appreciate any guidance on this.