Problem with foreign keys being NULLED after commit and refresh if you create object using ID of related object

[SMorawiec]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

Commit to Help

• I commit to help with one of those options 👆

Example Code

class Team(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

    heroes: list["Hero"] = Relationship(back_populates="team")


class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: int | None = Field(default=None, index=True)

    team_id: int | None = Field(default=None, foreign_key="team.id")
    team: Team | None = Relationship(back_populates="heroes")

@fixture
def fake_db_session():
    engine = create_engine(
        "sqlite://",
        connect_args={"check_same_thread": False},
        poolclass=StaticPool,
    )
    SQLModel.metadata.create_all(engine)

    with Session(engine) as session:
        yield session

class TestCreate:
    @staticmethod
    def test_create_location_to_location(fake_db_session: Session):
        team = Team(name="Test Team", headquarters="Test Headquarters")
        hero = Hero(name="Test Hero", secret_name="Test Secret Name", age=30, team_id=team.id)
        #hero = Hero(name="Test Hero", secret_name="Test Secret Name", age=30, team=team)
        hero_db = Hero.model_validate(hero)
        
        fake_db_session.add(team)
        fake_db_session.add(hero_db)
        fake_db_session.commit()
        fake_db_session.refresh(team)
        fake_db_session.refresh(hero_db)
        breakpoint()

Description

Im running very simple example code (basically taken from tutorial.
I thought there are 2 ways of creating relationship.- using team or team_id (One hero instance creating is commented out).
The problem is that when I run the code above, Relationship is not created, and team_id of object hero_db is NULL.
Removing model_validate from the code resolves the problem, but in more complex examples, it is required to properly parse input.
Am I doing something wrong or is it really bad bug? Because I cant imagine passing the entire objects instead of IDs is a must for bigger objects.

Operating System

macOS

Operating System Details

No response

SQLModel Version

Name: sqlmodel Version: 0.0.22

Python Version

Python 3.12.7

Additional Context

No response