👀 Views: 86 💬 Answers: 1 📅 Created: 2025-06-10

fastapi sqlalchemy asyncio orm Python

I'm experimenting with I've been banging my head against this for hours. I'm developing a FastAPI application using SQLAlchemy for ORM and I'm working with a peculiar scenario with async session handling. When I try to retrieve related objects from a parent entity using an async SQLAlchemy session, I encounter inconsistent results. Specifically, I have a simple model setup like this: ```python from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine from sqlalchemy.orm import sessionmaker, declarative_base, relationship Base = declarative_base() class Parent(Base): __tablename__ = 'parents' id = Column(Integer, primary_key=True) name = Column(String) children = relationship('Child', back_populates='parent') class Child(Base): __tablename__ = 'children' id = Column(Integer, primary_key=True) parent_id = Column(Integer, ForeignKey('parents.id')) parent = relationship('Parent', back_populates='children') ``` In my FastAPI route, I’m using an async function to fetch a parent and its children: ```python @app.get('/parent/{parent_id}') async def get_parent(parent_id: int, session: AsyncSession = Depends(get_session)): result = await session.get(Parent, parent_id) return result ``` However, when I call the endpoint to get a parent, the children list is sometimes empty, even though I know there are related records in the database. I’ve tried to debug this by logging the SQL queries being executed and confirming that the related children are indeed present in the database. I verified that the session is properly managed and I’m using SQLAlchemy 1.4.23 with FastAPI 0.68.0. I also tried using `await session.execute(select(Parent).options(selectinload(Parent.children)))` instead, but I still get inconsistent results. What could be causing this scenario? Are there any specific configurations or behaviors of async sessions in SQLAlchemy that I might be overlooking? Any insights or suggestions would be greatly appreciated. I'm working on a application that needs to handle this. Am I missing something obvious? Thanks, I really appreciate it!