I am trying to return connected data via foreign key in FastAPI but when I use a class in response_model that contains the data, the endpoint throws a greenlet error. I am using FastAPI and SQLModel (I know about the error with SQLModel relationships and SQLAlchemy and I downgrade to sqlalchemy 1.4.35). My code is the following:
models.py
class BaseQuestion(SQLModel):
survey_id: Optional[int] = Field(default=None, foreign_key="survey.id")
title: Optional[str] = Field(default=None, max_length=45)
help: Optional[str] = Field(default=None, max_length=45)
priority: Optional[int] = Field(default=None)
is_mandatory: Optional[int] = Field(default=None)
class Question(BaseQuestion, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
answers: List["Answer"] = Relationship(back_populates="question")
survey: Optional[Survey] = Relationship(back_populates="questions")
class QuestionOut(BaseQuestion):
id: Optional[int] = Field(default=None, primary_key=True)
class BaseAnswer(SQLModel):
question_id: Optional[int] = Field(default=None, foreign_key="question.id")
text: Optional[str] = Field(default=None, max_length=45)
help: Optional[str] = Field(default=None, max_length=45)
priority: Optional[str] = Field(default=None, max_length=45)
is_stoping: Optional[int] = Field(default=0)
class Answer(BaseAnswer, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
question: Optional[Question] = Relationship(back_populates="answers")
class AnswerOut(BaseAnswer):
id: Optional[int] = Field(default=None, primary_key=True)
class QuestionWithAnswer(QuestionOut):
answers: List[Answer] = []
api.py
@app.get("/questions/{question_id}", response_model=questionnaire.QuestionOut)
async def get_question(question_id: int, session: db.Session = Depends(session)):
db_question = await session.get(questionnaire.Question, question_id)
if not db_question:
raise HTTPException(status_code=404, detail="Question not found")
return db_question
db.py
def create_engine(host: str, username: str, password: str, name: str) -> AsyncEngine:
return create_async_engine(
URL.create(
drivername="mariadb+aiomysql",
host=host,
username=username,
password=password,
database=name,
),
)
def session_factory(app: FastAPI) -> Callable:
async def session() -> AsyncGenerator[Session, None]:
async with Session(app.state.engine) as session:
yield session
return session
And the error is:
concurrency_py3k.py", line 67, in await_only
survey-service-1 | raise exc.MissingGreenlet(
survey-service-1 | sqlalchemy.exc.StatementError: (sqlalchemy.exc.MissingGreenlet) greenlet_spawn has not been called; can't call await_() here. Was IO attempted in an unexpected place?
survey-service-1 | [SQL: SELECT answer.question_id AS answer_question_id, answer.text AS answer_text, answer.help AS answer_help, answer.priority AS answer_priority, answer.is_stoping AS answer_is_stoping, answer.id AS answer_id
survey-service-1 | FROM answer
survey-service-1 | WHERE %s = answer.question_id]
survey-service-1 | [parameters: [{'%(140173137451136 param)s': 1}]]
survey-service-1 | (Background on this error at: https://sqlalche.me/e/14/xd2s)
