级联删除关系¶
如果删除一个与英雄有关系的团队，会发生什么？
这些英雄是否也应该被自动删除？这被称为“级联”，因为初始删除会导致其他删除的级联。
他们的 team_id 应该在数据库中设置为 NULL 吗？
让我们看看如何用 SQLModel 配置它。
信息
此功能，包括 cascade_delete、ondelete 和 passive_deletes，从 SQLModel 0.0.21 版本开始提供。
初始的英雄和团队¶
假设我们有这些团队和英雄。
团队表¶
| id | name | 总部 |
|---|---|---|
| 1 | Z-部队 | 玛格丽特修女酒吧 |
| 2 | 阻止者 | 锐利之塔 |
| 3 | 瓦卡兰 | 瓦卡兰首都 |
英雄表¶
| id | name | secret_name | age | team_id |
|---|---|---|---|---|
| 1 | 死侍 | 戴夫·威尔逊 | 1 | |
| 2 | 锈人 | 汤米·夏普 | 48 | 2 |
| 3 | 蜘蛛男孩 | 佩德罗·帕尔克多 | 2 | |
| 4 | 黑狮 | 特雷弗·查拉 | 35 | 3 |
| 5 | 苏睿公主 | 苏睿 | 3 |
可视化团队和英雄¶
我们可以像这样可视化它们
flowchart TB
subgraph "Z-Force"
d("Deadpond")
end
subgraph "Preventers"
r("Rusty-Man")
s("Spider-Boy")
end
subgraph "Wakaland"
b("Black Lion")
p("Princess Sure-E")
end删除一个带有英雄的团队¶
当我们删除一个团队时，我们必须对相关的英雄做些什么。
默认情况下，它们指向团队的外键将在数据库中设置为 NULL。
但假设我们希望相关的英雄被自动删除。
例如，我们可以删除团队 Wakaland
flowchart TB
subgraph zforce["Z-Force"]
d("Deadpond")
end
subgraph preventers["Preventers"]
r("Rusty-Man")
s("Spider-Boy")
end
subgraph wakaland["Wakaland"]
b("Black Lion")
p("Princess Sure-E")
end
style wakaland fill:#fee,stroke:#900并且我们希望英雄 Black Lion 和 Princess Sure-E 也被自动删除。
所以我们最终会得到这些团队和英雄
flowchart TB
subgraph zforce["Team Z-Force"]
d("Deadpond")
end
subgraph preventers["Team Preventers"]
r("Rusty-Man")
s("Spider-Boy")
end配置自动删除¶
有两个地方可以配置此自动删除
- 在 Python 代码中
- 在数据库中
使用 cascade_delete 在 Python 中删除¶
创建 Relationship() 时，我们可以设置 cascade_delete=True。
这会配置 SQLModel 在初始记录被删除（一个团队）时自动删除相关记录（英雄）。
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", cascade_delete=True)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", cascade_delete=True)
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", ondelete="CASCADE")
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
通过此配置，当我们删除一个团队时，SQLModel（实际上是 SQLAlchemy）将
- 确保相关记录的对象已加载，在本例中是
heroes。如果未加载，它将向数据库发送SELECT查询以获取它们。 - 向数据库发送
DELETE查询，包括每个相关记录（每个英雄）。 - 最后，用另一个
DELETE查询删除初始记录（团队）。
这样，内部的 Python 代码将通过为每个相关记录发出必要的 SQL 查询来负责删除它们。
提示
cascade_delete 参数在 Relationship() 中设置，在没有外键的模型上。
技术细节
在 Relationship() 中设置 cascade_delete=True 将配置 SQLAlchemy 使用 cascade="all, delete-orphan"，这是在需要级联删除时最常见和有用的配置。
您可以在 SQLAlchemy 文档中阅读更多内容。
使用 ondelete 在数据库中删除¶
在上一节中，我们看到使用 cascade_delete 处理 Python 代码中的自动删除。
但是，如果有人直接与数据库交互，不使用我们的代码，而是使用 SQL 删除一个团队，会发生什么？
对于这些情况，我们可以通过在 Field() 中使用 ondelete 参数来配置数据库以自动删除相关记录。
ondelete 选项¶
ondelete 参数将在数据库中外键列中设置 SQL ON DELETE。
ondelete 可以有这些值
CASCADE：当相关记录（团队）被删除时，自动删除此记录（英雄）。SET NULL：当相关记录被删除时，将此外键（hero.team_id）字段设置为NULL。RESTRICT：如果存在外键值，则通过引发错误来阻止删除此记录（英雄）。
将 ondelete 设置为 CASCADE¶
如果我们希望配置数据库在父记录被删除时自动删除相关记录，我们可以设置 ondelete="CASCADE"。
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", cascade_delete=True)
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", ondelete="CASCADE")
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, select
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", cascade_delete=True)
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", ondelete="CASCADE")
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
现在，当我们在数据库中创建表时，Hero 表中的 team_id 列将在数据库级别具有 ON DELETE CASCADE 定义。
这将配置数据库在相关记录（团队）被删除时自动删除记录（英雄）。
提示
ondelete 参数在 Field() 中设置，在有外键的模型上。
使用 cascade_delete 或 ondelete¶
此时，您可能想知道是否应该使用 cascade_delete 或 ondelete。答案是：两者都用！🤓
ondelete 将配置数据库，以防有人直接与其交互。
但 cascade_delete 仍然需要告诉 SQLAlchemy 它应该删除内存中的 Python 对象。
外键约束支持¶
一些数据库不支持外键约束。
例如，SQLite 默认不支持它们。它们必须通过自定义 SQL 命令手动启用
PRAGMA foreign_keys = ON;
因此，通常同时配置 cascade_delete 和 ondelete 是个好主意。
提示
您将在下面的 passive_deletes 部分中了解如何禁用默认的自动 SQLModel（SQLAlchemy）行为并仅依赖于数据库。
Relationship() 上的 cascade_delete 和 Field() 上的 ondelete¶
只是一个提醒... 🤓
ondelete放在带有外键的Field()上。在“一对多”关系中的“多”方。
class Hero(SQLModel, table=True):
...
team_id: int = Field(foreign_key="team.id", ondelete="CASCADE")
cascade_delete放在Relationship()上。通常在“一对多”关系中的“一”方，即没有外键的一方。
class Team(SQLModel, table=True):
...
heroes: list[Hero] = Relationship(cascade_delete=True)
删除一个团队及其英雄¶
现在，当我们删除一个团队时，我们不需要做任何其他事情，它会自动地删除它的英雄。
# Code above omitted 👆
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", cascade_delete=True)
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", ondelete="CASCADE")
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
确认英雄已被删除¶
我们可以确认删除团队 Wakaland 后，英雄 Black Lion 和 Princess Sure-E 也已被删除。
如果我们尝试从数据库中选择它们，我们将不再找到它们。
# Code above omitted 👆
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", cascade_delete=True)
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", ondelete="CASCADE")
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", cascade_delete=True)
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", ondelete="CASCADE"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion not found:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E not found:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
运行带有 cascade_delete=True 和 ondelete="CASCADE" 的程序¶
我们可以通过运行程序来确认一切正常。
$ python app.py
// Some boilerplate and previous output omitted 😉
// The team table is created as before
CREATE TABLE team (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
headquarters VARCHAR NOT NULL,
PRIMARY KEY (id)
)
// The hero table is created with the ON DELETE CASCADE 🎉
// In SQLite, it also includes REFERENCES team (id), this is needed by SQLite to work with the ON DELETE CASCADE properly.
// SQLAlchemy takes care of setting it up for us to make sure it works 🤓
CREATE TABLE hero (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
secret_name VARCHAR NOT NULL,
age INTEGER,
team_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(team_id) REFERENCES team (id) ON DELETE CASCADE
)
// We select the team Wakaland
INFO Engine SELECT team.id, team.name, team.headquarters
FROM team
WHERE team.name = ?
INFO Engine [generated in 0.00014s] ('Wakaland',)
// Then, because of cascade_delete, right before deleting Wakaland, SQLAlchemy loads the heroes
INFO Engine SELECT hero.id AS hero_id, hero.name AS hero_name, hero.secret_name AS hero_secret_name, hero.age AS hero_age, hero.team_id AS hero_team_id
FROM hero
WHERE ? = hero.team_id
INFO Engine [generated in 0.00020s] (3,)
// Next, before deleting the Wakaland team, it sends a DELETE statement including each related hero: Black Lion and Princess Sure-E, with IDs 4 and 5
INFO Engine DELETE FROM hero WHERE hero.id = ?
INFO Engine [generated in 0.00022s] [(4,), (5,)]
// After that, it will send the delete for the team Wakaland with ID 3
INFO Engine DELETE FROM team WHERE team.id = ?
INFO Engine [generated in 0.00017s] (3,)
// Print the deleted team
Deleted team: name='Wakaland' id=3 headquarters='Wakaland Capital City'
// Finally, we try to select the heroes from Wakaland, Black Lion and Princess Sure-E and print them, but they are now deleted
Black Lion not found: None
Princess Sure-E not found: None
ondelete 与 SET NULL¶
我们可以配置数据库，使其在相关记录（在 team 表中）被删除时，将外键（在 hero 表中的 team_id）设置为 NULL。
在这种情况下，带有 Relationship() 的一方不会有 cascade_delete，但带有 Field() 和 foreign_key 的一方将有 ondelete="SET NULL"。
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", ondelete="SET NULL"
)
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, select
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", ondelete="SET NULL"
)
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", ondelete="SET NULL"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", ondelete="SET NULL"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
上述配置将 Hero 表中的 team_id 列设置为 ON DELETE SET NULL。
这样，当有人直接使用 SQL 从数据库中删除一个团队时，数据库将找到该团队的英雄，并将 team_id 设置为 NULL（如果数据库支持）。
提示
外键应该允许 None 值（数据库中的 NULL），否则您会因违反 NOT NULL 约束而遇到完整性错误。
所以 team_id 需要一个可以为 None 的类型，例如
team_id: int | None
不使用 ondelete="SET NULL"¶
如果您不使用 ondelete="SET NULL"，不在 cascade_delete 上设置任何内容，并删除一个团队，会发生什么？
默认行为是 SQLModel（实际上是 SQLAlchemy）会转到英雄并从 Python 代码中将其 team_id 设置为 NULL。
因此，默认情况下，这些 team_id 字段将设置为 NULL。
但是，如果有人进入数据库并手动删除一个团队，英雄的 team_id 可能会指向一个不存在的团队。
添加 ondelete="SET NULL" 会配置数据库本身也将这些字段设置为 NULL。
但是，如果您从代码中删除一个团队，默认情况下，SQLModel（实际上是 SQLAlchemy）会在数据库 SET NULL 生效之前更新这些 team_id 字段为 NULL。
使用 SET NULL 删除团队¶
删除团队的代码与之前相同，唯一改变的是数据库中底层的配置。
# Code above omitted 👆
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select
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", ondelete="SET NULL"
)
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()
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, 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", ondelete="SET NULL"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
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", ondelete="SET NULL"
)
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
结果将是这些表。
SET NULL 后的团队表¶
| id | name | 总部 |
|---|---|---|
| 1 | Z-部队 | 玛格丽特修女酒吧 |
| 2 | 阻止者 | 锐利之塔 |
SET NULL 后的英雄表¶
| id | name | secret_name | age | team_id |
|---|---|---|---|---|
| 1 | 死侍 | 戴夫·威尔逊 | 1 | |
| 2 | 锈人 | 汤米·夏普 | 48 | 2 |
| 3 | 蜘蛛男孩 | 佩德罗·帕尔克多 | 2 | |
| 4 | 黑狮 | 特雷弗·查拉 | 35 | 空 |
| 5 | 苏睿公主 | 苏睿 | 空 |
SET NULL 后可视化团队和英雄¶
我们可以像这样可视化它们
flowchart TB
subgraph "Z-Force"
d("Deadpond")
end
subgraph "Preventers"
r("Rusty-Man")
s("Spider-Boy")
end
b("Black Lion")
p("Princess Sure-E")运行带有 SET NULL 的程序¶
现在让我们运行程序来确认一切正常
$ python app.py
// Some boilerplate and previous output omitted 😉
// The hero table is created with the ON DELETE SET NULL 🎉
// In SQLite, it also includes: REFERENCES team (id). This REFERENCES is needed by SQLite to work with the ON DELETE CASCADE properly.
// SQLModel with SQLAlchemy takes care of setting it up for us to make sure it works 🤓
CREATE TABLE hero (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
secret_name VARCHAR NOT NULL,
age INTEGER,
team_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(team_id) REFERENCES team (id) ON DELETE SET NULL
)
// We select the team Wakaland
INFO Engine SELECT team.id, team.name, team.headquarters
FROM team
WHERE team.id = ?
INFO Engine [generated in 0.00010s] (3,)
Team Wakaland: id=3 name='Wakaland' headquarters='Wakaland Capital City'
// Then, right before deleting Wakaland, the heroes are loaded automatically
INFO Engine SELECT hero.id AS hero_id, hero.name AS hero_name, hero.secret_name AS hero_secret_name, hero.age AS hero_age, hero.team_id AS hero_team_id
FROM hero
WHERE ? = hero.team_id
INFO Engine [generated in 0.00020s] (3,)
// Next, before deleting the Wakaland team, it sends an UPDATE statement including each related hero: Black Lion and Princess Sure-E, with IDs 4 and 5, to set their team_id to NULL. This is not the SET NULL we added, this is just the default SQLModel (SQLAlchemy) behavior.
INFO Engine UPDATE hero SET team_id=? WHERE hero.id = ?
INFO Engine [generated in 0.00009s] [(None, 4), (None, 5)]
// After that, it will send the delete for the team Wakaland with ID 3
INFO Engine DELETE FROM team WHERE team.id = ?
INFO Engine [generated in 0.00017s] (3,)
// Print the deleted team
Deleted team: name='Wakaland' id=3 headquarters='Wakaland Capital City'
// Finally, we select the heroes Black Lion and Princess Sure-E and print them, they no longer have a team
Black Lion has no team: age=35 id=4 name='Black Lion' secret_name='Trevor Challa' team_id=None
Princess Sure-E has no team: age=None id=5 name='Princess Sure-E' secret_name='Sure-E' team_id=None
团队 Wakaland 被删除，其所有英雄都失去了团队，换句话说，他们的 team_id 被设置为 NULL，但仍然保留在数据库中！🤓
让数据库使用 passive_deletes 来处理¶
在前面的例子中，我们使用 CASCADE 和 SET NULL 配置了 ondelete，以便数据库自动处理相关记录的删除。但我们实际上从未使用过该功能，因为 SQLModel (SQLAlchemy) 默认会加载相关记录并在发送团队的 DELETE 命令之前删除它们或将其更新为 NULL。
如果您知道您的数据库仅通过 ondelete="CASCADE" 或 ondelete="SET NULL" 就能正确处理自身的删除或更新，您可以在 Relationship() 中使用 passive_deletes="all" 来告诉 SQLModel (实际上是 SQLAlchemy) 在发送团队的 DELETE 命令之前不要删除或更新这些记录（对于英雄）。
在 SQLite 中启用外键支持¶
为了在 SQLite 中测试这个，我们首先需要启用外键支持。
# Code above omitted 👆
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
信息
您可以在 SQLAlchemy 文档中了解更多关于 SQLite、外键和此 SQL 命令的信息。
使用 passive_deletes="all"¶
现在让我们更新 Team 的表模型，在英雄的 Relationship() 中使用 passive_deletes="all"。
我们还将在 Hero 模型表的 team_id 外键 Field() 中使用 ondelete="SET NULL"，以使数据库自动将这些字段设置为 NULL。
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_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, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="SET NULL"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
运行带有 passive_deletes 的程序¶
现在，如果我们运行程序，我们会看到 SQLModel (SQLAlchemy) 不再加载和更新英雄，它只是发送团队的 DELETE。
$ python app.py
// Some boilerplate and previous output omitted 😉
// The hero table is created with the ON DELETE SET NULL as before
CREATE TABLE hero (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
secret_name VARCHAR NOT NULL,
age INTEGER,
team_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(team_id) REFERENCES team (id) ON DELETE SET NULL
)
// For SQLite, we also send the custom command to enable foreign key support
INFO Engine PRAGMA foreign_keys=ON
// We select and print the team Wakaland
Team Wakaland: id=3 name='Wakaland' headquarters='Wakaland Capital City'
// We won't see another SELECT for the heroes, nor an UPDATE or DELETE. SQLModel (with SQLAlchemy) won't try to load and update (or delete) the related records for heroes, it will just send the DELETE for the team right away.
INFO Engine DELETE FROM team WHERE team.id = ?
INFO Engine [generated in 0.00013s] (3,)
// At this point, because we enabled foreign key support for SQLite, the database will take care of updating the records for heroes automatically, setting their team_id to NULL
// Print the deleted team
Deleted team: name='Wakaland' id=3 headquarters='Wakaland Capital City'
// Finally, we select the heroes Black Lion and Princess Sure-E and print them, they no longer have a team
Black Lion has no team: age=35 id=4 name='Black Lion' secret_name='Trevor Challa' team_id=None
Princess Sure-E has no team: age=None id=5 name='Princess Sure-E' secret_name='Sure-E' team_id=None
ondelete 与 RESTRICT¶
我们还可以配置数据库，以阻止删除一条记录（一个团队），如果存在相关记录（英雄）。
在这种情况下，当有人尝试删除一个带有英雄的团队时，数据库将引发错误。
而且由于这是在数据库中配置的，即使有人直接使用 SQL 与数据库交互，也会发生这种情况（如果数据库支持）。
提示
对于 SQLite，这还需要启用外键支持。
在 SQLite 中为 RESTRICT 启用外键支持¶
由于 ondelete="RESTRICT" 主要是一个数据库级别的约束，我们首先在 SQLite 中启用外键支持，以便能够测试它。
# Code above omitted 👆
def create_db_and_tables():
SQLModel.metadata.create_all(engine)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
🤓 其他版本和变体
from typing import Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
使用 ondelete="RESTRICT"¶
让我们在 Hero 模型表的 team_id 外键 Field() 中设置 ondelete="RESTRICT"。
在 Team 模型表中，我们将在英雄的 Relationship() 中使用 passive_deletes="all"，这样将禁用从已删除模型设置外键为 NULL 的默认行为，并且当我们尝试删除一个带有英雄的团队时，数据库将引发错误。
提示
请注意，我们没有在 Team 模型表中设置 cascade_delete。
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
🤓 其他版本和变体
from typing import Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
delete_team()
if __name__ == "__main__":
main()
运行带有 RESTRICT 的程序，查看错误¶
现在，如果我们运行程序并尝试删除一个带有英雄的团队，我们将看到一个错误。
$ python app.py
// Some boilerplate and previous output omitted 😉
// The hero table is created with the ON DELETE RESTRICT
CREATE TABLE hero (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
secret_name VARCHAR NOT NULL,
age INTEGER,
team_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(team_id) REFERENCES team (id) ON DELETE RESTRICT
)
// Now, when we reach the point of deleting a team with heroes, we will see an error
Traceback (most recent call last):
File "/home/user/code...
sqlite3.IntegrityError: FOREIGN KEY constraint failed
// More error output here...
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) FOREIGN KEY constraint failed
[SQL: DELETE FROM team WHERE team.id = ?]
[parameters: (3,)]
太好了！数据库没有让我们犯删除带有英雄的团队的错误。🤓
提示
如果您想测试 PRAGMA foreign_keys=ON 是否必要，请注释掉那一行并再次运行，您将看不到错误。😱
passive_deletes="all" 也是如此，如果您注释掉那一行，SQLModel（SQLAlchemy）将在删除团队之前加载并更新英雄，将其外键 team_id 设置为 NULL，并且约束将无法按预期工作，您将看不到错误。😅
在删除团队之前更新英雄¶
在设置了 ondelete="RESTRICT"，配置 SQLite 支持外键，并在 Relationship() 中使用 passive_deletes="all" 之后，如果我们尝试删除一个带有英雄的团队，我们将看到一个错误。
如果我们想删除团队，我们需要先更新英雄并将其 team_id 设置为 None（或数据库中的 NULL）。
通过调用列表的 .clear() 方法，我们可以删除其所有项目。因此，通过调用 team.heroes.clear() 并将其保存到数据库，我们解除了英雄与团队的关联，这将把他们的 team_id 设置为 None。
提示
调用 team.heroes.clear() 与我们未配置 passive_deletes="all" 时 SQLModel（实际上是 SQLAlchemy）所做的非常相似。
# Code above omitted 👆
def remove_team_heroes():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
team.heroes.clear()
session.add(team)
session.commit()
session.refresh(team)
print("Team with removed heroes:", team)
# Code below omitted 👇
👀 完整文件预览
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def remove_team_heroes():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
team.heroes.clear()
session.add(team)
session.commit()
session.refresh(team)
print("Team with removed heroes:", team)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
remove_team_heroes()
delete_team()
select_deleted_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, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def remove_team_heroes():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
team.heroes.clear()
session.add(team)
session.commit()
session.refresh(team)
print("Team with removed heroes:", team)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
remove_team_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, text
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", passive_deletes="all")
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", ondelete="RESTRICT"
)
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)
with engine.connect() as connection:
connection.execute(text("PRAGMA foreign_keys=ON")) # for SQLite only
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)
def remove_team_heroes():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
team.heroes.clear()
session.add(team)
session.commit()
session.refresh(team)
print("Team with removed heroes:", team)
def delete_team():
with Session(engine) as session:
statement = select(Team).where(Team.name == "Wakaland")
team = session.exec(statement).one()
session.delete(team)
session.commit()
print("Deleted team:", team)
def select_deleted_heroes():
with Session(engine) as session:
statement = select(Hero).where(Hero.name == "Black Lion")
result = session.exec(statement)
hero = result.first()
print("Black Lion has no team:", hero)
statement = select(Hero).where(Hero.name == "Princess Sure-E")
result = session.exec(statement)
hero = result.first()
print("Princess Sure-E has no team:", hero)
def main():
create_db_and_tables()
create_heroes()
remove_team_heroes()
delete_team()
select_deleted_heroes()
if __name__ == "__main__":
main()
运行先删除英雄的程序¶
现在，如果我们运行程序并首先删除英雄，我们将能够毫无问题地删除团队。
$ python app.py
// Some boilerplate and previous output omitted 😉
// The hero table is created with the ON DELETE RESTRICT
CREATE TABLE hero (
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
secret_name VARCHAR NOT NULL,
age INTEGER,
team_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(team_id) REFERENCES team (id) ON DELETE RESTRICT
)
// We manually disassociate the heroes from the team
INFO Engine UPDATE hero SET team_id=? WHERE hero.id = ?
INFO Engine [generated in 0.00008s] [(None, 4), (None, 5)]
// We print the team from which we removed heroes
Team with removed heroes: name='Wakaland' id=3 headquarters='Wakaland Capital City'
// Now we can delete the team
INFO Engine DELETE FROM team WHERE team.id = ?
INFO Engine [generated in 0.00008s] (3,)
INFO Engine COMMIT
Deleted team: name='Wakaland' id=3 headquarters='Wakaland Capital City'
// The heroes Black Lion and Princess Sure-E are no longer associated with the team
Black Lion has no team: secret_name='Trevor Challa' name='Black Lion' team_id=None age=35 id=4
Princess Sure-E has no team: secret_name='Sure-E' name='Princess Sure-E' team_id=None age=None id=5
总结¶
在许多情况下，您实际上不需要配置任何东西。😎
在某些情况下，当您希望将记录的删除级联到其相关记录时（删除一个团队及其英雄），您可以
- 在没有外键的一侧的
Relationship()中使用cascade_delete=True - 并在带有外键的
Field()中使用ondelete="CASCADE"
这将涵盖大多数用例。🚀
如果您需要其他功能，可以参考上面描述的其他选项。🤓