Can't return result from session.exec directly (have to assign to an intermediate variable)?

[EarthStoodStill]

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• I already checked if it is not related to SQLModel but to SQLAlchemy.

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Example Code

I now know from the examples (after looking more) that you always assign the result from session.exec calls to a var of some Pydantic model type before returning anything from a function, but I'm still curious why the former doesn't work below (but the latter does). Can I get some info (maybe which library leads to this behavior, and where I can look to learn more about why this is needed, or what I can search for to read some more, since they appeared functionally equivalent to me).

# DOESN'T WORK -- causes an internal 500 error/session.exec(...) returns None
@app.get(f'/organizations/', response_model=List[models.Organization])
def read_organizations() -> List[models.Organization]:
    with Session(engine) as session:
        return session.exec(
            select(models.Organization)
        ).all()

vs.

# WORKS (returns list of organizations)
@app.get(f'/organizations/', response_model=List[models.Organization])
def read_organizations() -> List[models.Organization]:
    with Session(engine) as session:
        organizations: List[models.Organization] = session.exec(
            select(models.Organization)
        ).all()

        return organizations

Description

Just trying to get back all "organizations" instead of a single one. Something about my code structure in the former code is maybe returning from session.exec(...) before it has data, or is breaking it (but this is synchronous, so I wouldn't think that's the case)? I noticed you always assign to an intermediate variable before returning anything, so hopefully you know why/can point me to something I can read/Google about.

Operating System

Linux

Operating System Details

No response

SQLModel Version

0.0.18

Python Version

3.12

Additional Context

Thank you! Sorry if this is just a dumb variable scope/Python code structure issue -- I'm a bit rusty atm.

[EarthStoodStill]

p.s., I suppose the Pydantic types are being constructed from the result data -- maybe that's the answer. I wasn't expecting that to be necessary since I passed the type to the embedded select(...) (so maybe they don't come back as my custom Pyndatic types from session.exec(...)?)

[YuriiMotov]

There shouldn't be any difference. Could you provide MRE?

from typing import List

from fastapi import FastAPI
from sqlalchemy import StaticPool
from sqlmodel import Field, Session, SQLModel, create_engine, select


class Organization(SQLModel, table=True):
    id: int = Field(default=None, primary_key=True)
    name: str


# Create an in-memory SQLite database
connect_args = {"check_same_thread": False}
engine = create_engine(
    "sqlite:///:memory:", connect_args=connect_args, poolclass=StaticPool
)
SQLModel.metadata.create_all(engine)

with Session(engine) as session:
    session.add(Organization(name="Example Org"))
    session.add(Organization(name="Example Org 2"))
    session.add(Organization(name="Example Org 3"))
    session.commit()

app = FastAPI()


@app.get("/organizations/")
def read_organizations() -> List[Organization]:
    with Session(engine) as session:
        return session.exec(select(Organization)).all()