定义关系属性¶
现在我们终于进入了 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 | 总部 |
|---|---|---|
| 1 | 阻止者 | 锐利之塔 |
| 2 | Z-部队 | 玛格丽特修女酒吧 |
和一个 hero 表
| id | name | secret_name | age | team_id |
|---|---|---|---|---|
| 1 | 死侍 | 戴夫·威尔逊 | 空 | 2 |
| 2 | 锈人 | 汤米·夏普 | 48 | 1 |
| 3 | 蜘蛛男孩 | 佩德罗·帕尔克多 | 空 | 1 |
现在您已经了解这些表在底层如何工作以及模型类如何表示它们，是时候添加一些便利功能了，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，我们只在用 select() 查询时使用 team_id 列连接表
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
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
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，都代表表中的一列。
但现在让我们给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
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine
# Code below omitted 👇
👀 完整文件预览
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
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 Relationship 在模型类中声明一个新属性
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
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
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，它们的值不是像整数一样的单一值。它们的值是实际相关的整个对象。
因此，对于一个 Hero 实例，如果您调用 hero.team，您将获得该英雄所属的整个 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)
关系属性或 None¶
请注意，在 Hero 类中，team 的类型注解是 Team | None。
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 实例必须属于一个 Team，那么 team_id 将是 int 而不是 int | None，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 Team | None。
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，因为它将包含这些对象。
SQLModel（实际上是 SQLAlchemy）足够智能，知道关系是通过 team_id 建立的，因为那是从 hero 表指向 team 表的外键，所以我们不需要在这里明确指定。
提示
在接下来的几章中，我们还会再次检查一些关于 list["Hero"] 和 back_populates 的内容。
但现在，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看一些如何使用这些新的关系属性的实际示例。✨