定义关系属性

现在我们终于来到了 SQLModel 最激动人心的部分之一。

关系属性。 ✨

我们目前有一个 team 表

id	name	headquarters
1	Preventers	Sharp Tower
2	Z-Force	Sister Margaret's Bar

和一个 hero 表

id	name	secret_name	age	team_id
1	Deadpond	Dive Wilson	null	2
2	Rusty-Man	Tommy Sharp	48	1
3	Spider-Boy	Pedro Parqueador	null	1

既然您了解了这些表在底层的运作方式以及模型类如何表示它们，那么现在是时候添加一些便利性，这将使代码中的许多操作更简单。

声明关系属性

到目前为止，我们在使用 select() 查询时，仅使用 team_id 列来连接表

Python 3.10+

from sqlmodel import Field, Session, SQLModel, create_engine


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


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")

# Code below omitted 👇

👀 完整文件预览

Python 3.10+

from sqlmodel import Field, Session, SQLModel, create_engine


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


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")


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")
        session.add(team_preventers)
        session.add(team_z_force)
        session.commit()

        hero_deadpond = Hero(
            name="Deadpond", secret_name="Dive Wilson", team_id=team_z_force.id
        )
        hero_rusty_man = Hero(
            name="Rusty-Man",
            secret_name="Tommy Sharp",
            age=48,
            team_id=team_preventers.id,
        )
        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)


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

🤓 其他版本和变体

Python 3.8+

from typing import Optional

from sqlmodel import Field, Session, SQLModel, create_engine


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


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")


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")
        session.add(team_preventers)
        session.add(team_z_force)
        session.commit()

        hero_deadpond = Hero(
            name="Deadpond", secret_name="Dive Wilson", team_id=team_z_force.id
        )
        hero_rusty_man = Hero(
            name="Rusty-Man",
            secret_name="Tommy Sharp",
            age=48,
            team_id=team_preventers.id,
        )
        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)


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

这是一个 普通字段，像所有其他字段一样，都表示 表中的一列。

但是现在让我们为这些模型类添加几个新的特殊属性，让我们添加 Relationship 属性。

首先，从 sqlmodel 导入 Relationship

Python 3.10+

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

# Code below omitted 👇

👀 完整文件预览

Python 3.10+

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


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")


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

🤓 其他版本和变体

Python 3.9+Python 3.8+

from typing import Optional

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


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

from typing import List, Optional

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


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

接下来，使用该 Relationship 在模型类中声明一个新属性

Python 3.10+

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


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")

# Code below omitted 👇

👀 完整文件预览

Python 3.10+

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


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")


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

🤓 其他版本和变体

Python 3.9+Python 3.8+

from typing import Optional

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


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

from typing import List, Optional

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


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()


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

什么是这些关系属性

这些新属性与字段不同，它们不直接表示数据库中的列，并且它们的值不是像整数这样的单个值。它们的值是相关的实际整个对象。

因此，在 Hero 实例的情况下，如果您调用 hero.team，您将获得此英雄所属的整个 Team 实例对象。 ✨

例如，您可以检查一个 hero 是否属于任何 team（如果 .team 不是 None），然后打印团队的 name

if hero.team:
    print(hero.team.name)

可选的关系属性

请注意，在 Hero 类中，team 的类型注解是 Optional[Team]。

这意味着此属性可以是 None，也可以是完整的 Team 对象。

这是因为相关的 team_id 也可以是 None（或数据库中的 NULL）。

如果 Hero 实例必须属于 Team，那么 team_id 将是 int 而不是 Optional[int]，它的 Field 将是 Field(foreign_key="team.id") 而不是 Field(default=None, foreign_key="team.id")，并且 team 属性将是 Team 而不是 Optional[Team]。

带有列表的关系属性

在 Team 类中，heroes 属性被注解为 Hero 对象的列表，因为这将是它所拥有的。

SQLModel（实际上是 SQLAlchemy）足够智能，知道关系是由 team_id 建立的，因为那是从 hero 表指向 team 表的外键，所以我们不必在此处显式指定它。

提示

在接下来的章节中，我们将再次检查一些关于 list["Hero"] 和 back_populates 的内容。

但现在，让我们首先看看如何使用这些关系属性。

下一步

现在，让我们在接下来的章节中看到一些关于如何使用这些新的 关系属性 的真实示例。 ✨