SQLModel运行官方示例报'Team'对象无'heroes'属性错误

我正在学习Tiangolo开发的SQLModel库，尝试运行官方文档关系属性读取章节的示例代码，对应文档地址：SQLModel 关系属性读取教程

使用的示例代码如下：

from typing import List, Optional

from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select


class Team(SQLModel, table=True):
    id: Optional[int] = 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: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)

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


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

engine = create_engine(sqlite_url, echo=True)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


def create_heroes():
    with Session(engine) as session:
        team_preventers = Team(name="Preventers", headquarters="Sharp Tower")
        team_z_force = Team(name="Z-Force", headquarters="Sister Margaret’s Bar")

        hero_deadpond = Hero(
            name="Deadpond", secret_name="Dive Wilson", team=team_z_force
        )
        hero_rusty_man = Hero(
            name="Rusty-Man", secret_name="Tommy Sharp", age=48, team=team_preventers
        )
        hero_spider_boy = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
        session.add(hero_deadpond)
        session.add(hero_rusty_man)
        session.add(hero_spider_boy)
        session.commit()

        session.refresh(hero_deadpond)
        session.refresh(hero_rusty_man)
        session.refresh(hero_spider_boy)

        print("Created hero:", hero_deadpond)
        print("Created hero:", hero_rusty_man)
        print("Created hero:", hero_spider_boy)

        hero_spider_boy.team = team_preventers
        session.add(hero_spider_boy)
        session.commit()
        session.refresh(hero_spider_boy)
        print("Updated hero:", hero_spider_boy)

        hero_black_lion = Hero(name="Black Lion", secret_name="Trevor Challa", age=35)
        hero_sure_e = Hero(name="Princess Sure-E", secret_name="Sure-E")
        team_wakaland = Team(
            name="Wakaland",
            headquarters="Wakaland Capital City",
            heroes=[hero_black_lion, hero_sure_e],
        )
        session.add(team_wakaland)
        session.commit()
        session.refresh(team_wakaland)
        print("Team Wakaland:", team_wakaland)

        hero_tarantula = Hero(name="Tarantula", secret_name="Natalia Roman-on", age=32)
        hero_dr_weird = Hero(name="Dr. Weird", secret_name="Steve Weird", age=36)
        hero_cap = Hero(
            name="Captain North America", secret_name="Esteban Rogelios", age=93
        )

        team_preventers.heroes.append(hero_tarantula)
        team_preventers.heroes.append(hero_dr_weird)
        team_preventers.heroes.append(hero_cap)
        session.add(team_preventers)
        session.commit()
        session.refresh(hero_tarantula)
        session.refresh(hero_dr_weird)
        session.refresh(hero_cap)
        print("Preventers new hero:", hero_tarantula)
        print("Preventers new hero:", hero_dr_weird)
        print("Preventers new hero:", hero_cap)


def select_heroes():
    with Session(engine) as session:
        statement = select(Hero).where(Hero.name == "Spider-Boy")
        result = session.exec(statement)
        hero_spider_boy = result.one()

        statement = select(Team).where(Team.id == hero_spider_boy.id)
        result = session.exec(statement)
        team = result.first()
        print("Spider-Boy's team:", team)

        print("Spider-Boy's team again:", hero_spider_boy.team)


def main():
    create_db_and_tables()
    create_heroes()
    select_heroes()


if __name__ == "__main__":
    main()

运行时抛出如下报错：

File "example.py", line 83, in create_heroes
    team_preventers.heroes.append(hero_tarantula)
AttributeError: 'Team' object has no attribute 'heroes'

运行环境为Python 3.9，SQLModel版本为0.0.6。Team类中已经明确定义了heroes关系属性，不清楚遗漏了什么配置，需要找到报错原因和解决方法。

这是SQLModel 0.0.6版本的已知bug：执行session.commit()操作后，没有被显式refresh()的ORM实例，其定义的关系属性会被清空失效。
你的代码中，team_preventers实例在第一次commit后从未被执行过refresh操作，后续多次commit后这个实例的关系属性已经丢失，自然访问不到heroes属性。
另外你贴的示例代码里还有一处逻辑错误：select_heroes函数中查询所属队伍的条件写为Team.id == hero_spider_boy.id，正确条件应该是Team.id == hero_spider_boy.team_id，否则查出来的不是Spider-Boy所属的队伍。

• 临时修复（不需要升级版本）：在操作team_preventers.heroes之前，加一行session.refresh(team_preventers)，从数据库重新加载实例的所有属性（包括关系属性），即可正常访问heroes列表。
• 彻底修复：将SQLModel升级到0.0.8及以上版本，新版本已经修复了commit后实例关系属性丢失的问题，不需要额外手动refresh即可正常操作关系属性。
• 额外注意：修复完上述报错后，记得修改select_heroes里的查询条件，否则会得到错误的队伍查询结果。

内容的提问来源于stack exchange，提问作者ibi0tux