FastAPI with SQLAlchemy and nested relationships causing 500 Internal Server Error
I've hit a wall trying to I'm building a REST API using FastAPI with SQLAlchemy and I'm encountering a 500 Internal Server Error when trying to retrieve data from a nested relationship. I have two models, `User` and `Post`, where a user can have multiple posts. The models are defined as follows: ```python from sqlalchemy import Column, Integer, String, ForeignKey from sqlalchemy.orm import relationship from database import Base class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True, index=True) name = Column(String, index=True) posts = relationship('Post', back_populates='owner') class Post(Base): __tablename__ = 'posts' id = Column(Integer, primary_key=True, index=True) title = Column(String, index=True) content = Column(String) owner_id = Column(Integer, ForeignKey('users.id')) owner = relationship('User', back_populates='posts') ``` I have created an endpoint to fetch a user along with their posts using the following code: ```python from fastapi import FastAPI, HTTPException from sqlalchemy.orm import Session from models import User, Post from database import get_db app = FastAPI() @app.get('/users/{user_id}') async def read_user(user_id: int, db: Session = Depends(get_db)): user = db.query(User).filter(User.id == user_id).first() if not user: raise HTTPException(status_code=404, detail='User not found') return user ``` When I access the endpoint with a valid user ID, I receive a 500 error with the following traceback: ``` ERROR: Exception in ASGI application Traceback (most recent call last): ... File "/usr/local/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 240, in get del self.impl[key] KeyError: 'owner' ``` I suspect it might be related to how the SQLAlchemy relationships are being loaded. I’ve tried modifying the endpoint to use `joinedload` to eagerly fetch posts, but that hasn't resolved the issue. Here's what I attempted: ```python from sqlalchemy.orm import joinedload @app.get('/users/{user_id}') async def read_user(user_id: int, db: Session = Depends(get_db)): user = db.query(User).options(joinedload(User.posts)).filter(User.id == user_id).first() if not user: raise HTTPException(status_code=404, detail='User not found') return user ``` However, I still encounter the same 500 Internal Server Error. Any insights on how to correctly fetch the user along with their posts without triggering this error would be greatly appreciated. I'm using FastAPI version 0.65.2 and SQLAlchemy version 1.4.22. Thanks! Has anyone else encountered this? Am I approaching this the right way?