👀 Views: 67 💬 Answers: 1 📅 Created: 2025-07-16

Flask SQLAlchemy asyncio Python

I'm working with an scenario with my Flask application where an async route that interacts with a SQLAlchemy database is consistently returning a 500 behavior. My route is defined with async/await syntax, but it seems that SQLAlchemy is causing issues. Here’s a simplified version of my code: ```python from flask import Flask, jsonify from flask_sqlalchemy import SQLAlchemy import asyncio app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db' db = SQLAlchemy(app) class User(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(50), nullable=False) @app.route('/users', methods=['GET']) async def get_users(): users = await db.session.execute(db.select(User)) return jsonify([{'id': user.id, 'name': user.name} for user in users.scalars()]) if __name__ == '__main__': db.create_all() # Ensure the database is created app.run(debug=True) ``` When I hit the `/users` endpoint, I get a 500 Internal Server behavior. In the terminal, I see this traceback: ``` Traceback (most recent call last): File "app.py", line 25, in get_users users = await db.session.execute(db.select(User)) File "sqlalchemy/ext/asyncio/session.py", line 350, in execute result = await self._execute(<...>) # truncated for brevity TypeError: object of type 'Session' has no len() ``` I’ve tried adding `await` to the `db.session` methods and also considered replacing the synchronous session with an async session, but it seems I might be misunderstanding how to use SQLAlchemy with Flask's async capabilities. I am currently using Flask 2.0.2 and SQLAlchemy 1.4.23. Can someone guide to understand what's going wrong and how to properly implement an async route with SQLAlchemy in Flask?