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1. syncopatedNote

   added

   questionFurther information is requestedFurther information is requested

   on Jul 21, 2022
2. Apollo314 commented on Jul 22, 2022

   

   Apollo314

   on Jul 22, 2022

   More actions

   Probably has something to do with SQLAlchemy version. After SQLAlchemy version 1.4.35, relationships have been broken. #315

   Reacted by Vishal and markzhang0928
3. cisaacstern commented on Jul 24, 2022

   

   cisaacstern

   on Jul 24, 2022

   More actions

   I agree with @Apollo314's assessment. We are also seeing this problem in our project, and pinning sqlalchemy==1.4.35 solves the problem, as documented in #315.

   Reacted by Vishal, 20-100, Andrew and Jones Wan
4. syncopatedNote commented on Jul 25, 2022

   

   syncopatedNote

   on Jul 25, 2022

   Author

   More actions

   Thanks a lot folks. I will try downgrading to .35 and see how that goes. M sure thats the reason, because thats the only thing that made sense so far while debugging. Appreciate the help.
5. guysoft

   added a commit that references this issue on Apr 13, 2023

   Fix relationships that are broken in newer versions of sqlmodel fasta…

   97fd35f
6. YuriiMotov commented on Aug 7, 2025

   

   YuriiMotov

   on Aug 7, 2025

   Member

   More actions

   It was fixed by #461.
   It works well in current version (SQLModel 0.0.24, SQLAlchemy 2.0.42)

   Test code in the details:

   Details

   from contextlib import asynccontextmanager
   from typing import Optional, cast
   
   from fastapi import Depends, FastAPI, HTTPException, Request
   from fastapi.testclient import TestClient
   from sqlalchemy import Engine, StaticPool
   from sqlmodel import Field, Relationship, Session, SQLModel, create_engine
   
   
   class TripInput(SQLModel):
       start: int
       end: int
       description: str
   
   
   class TripOutput(TripInput):
       id: int
   
   
   class Trip(TripInput, table=True):
       id: Optional[int] = Field(default=None, primary_key=True)
       car_id: int = Field(foreign_key="car.id")
       car: "Car" = Relationship(back_populates="trips")
   
   
   class CarInput(SQLModel):
       size: str
       fuel: str = "electric"
       doors: int
       transmission: str = "auto"
   
   
   class Car(CarInput, table=True):
       id: Optional[int] = Field(primary_key=True, default=None)
       trips: list[Trip] = Relationship(back_populates="car")
   
   
   class CarOutput(CarInput):
       id: int
       trips: list[TripOutput] = []
   
   
   def init_db(engine: Engine):
       SQLModel.metadata.create_all(engine)
       with Session(engine) as session:
           session.add(Car(size="m", fuel="hybrid", doors=4, id=1))
           session.add(Car(size="l", fuel="hybrid", doors=5, id=2))
           session.add(Trip(start=0, end=100, description="manali trip", id=1, car_id=1))
           session.add(Trip(start=300, end=600, description="Leh", id=2, car_id=1))
           session.add(Trip(start=0, end=20, description="Mall Visit", id=3, car_id=2))
           session.commit()
   
   
   @asynccontextmanager
   async def lifespan(app: FastAPI):
       engine = create_engine(
           "sqlite:///",
           connect_args={"check_same_thread": False},
           poolclass=StaticPool,
       )
       init_db(engine)
       yield {"engine": engine}
   
   
   app = FastAPI(lifespan=lifespan)
   
   
   async def get_session(request: Request):
       engine = cast(Engine, request.state._state["engine"])
       with Session(engine) as session:
           yield session
   
   
   @app.get("/api/cars/{id}", response_model=CarOutput)
   def car_by_id(id: int, session: Session = Depends(get_session)) -> Car:
       car = session.get(Car, id)
       if car:
           # query = select(Trip).where(Trip.car_id == id)
           # triplist = session.exec(query).all()
           # car.trips.append(triplist)
           return car
       else:
           raise HTTPException(status_code=400, detail=f"No car with id {id} found")
   
   
   def test_():
       with TestClient(app) as client:
           resp = client.get("/api/cars/1")
           assert resp.status_code == 200
           trips = resp.json()["trips"]
           assert len(trips) == 2
           assert trips[0]["description"] in ("manali trip", "Leh")

   BTW, you don't need to manually fetch trips and add them to car.trips

   @app.get("/api/cars/{id}", response_model=CarOutput)
   def car_by_id(id: int, session: Session = Depends(get_session)) -> Car:
       car = session.get(Car, id)
       if car:
           # query = select(Trip).where(Trip.car_id == id)
           # triplist = session.exec(query).all()
           # car.trips.append(triplist)
           return car
       else:
           raise HTTPException(status_code=400, detail=f"No car with id {id} found")
7. YuriiMotov

   closed this as completedon Aug 7, 2025