自动生成的 ID、None 默认值和数据刷新¶
在上一章中，我们学习了如何使用 SQLModel 向数据库添加行。
现在，让我们详细探讨一下为什么 id 字段在数据库中作为 主键 时 不能为 NULL，这是因为我们通过 Field(primary_key=True) 声明它。
然而，在 Python 代码中，同一个 id 字段实际上 可以是 None。因此，我们使用 int | None（或 Optional[int]）声明其类型，并设置默认值为 Field(default=None)：
# 上方代码省略 👆
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
# 下方代码省略 👇
# 上方代码省略 👆
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
接下来，我将详细介绍数据库与 Python 代码之间的数据同步。
比如，什么时候会从数据库中获取 id 字段的实际 int 值？让我们一起来探讨这些内容。👇
创建一个新的 Hero 实例¶
当我们创建一个新的 Hero 实例时，我们并没有设置 id：
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
# 下方代码省略 👇
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
Optional 如何帮助¶
由于我们没有设置 id，它会采用我们在 Field(default=None) 中设置的 Python 默认值 None。
这就是为什么我们使用 Optional 并将默认值设置为 None 的唯一原因。
因为在代码的这一部分，在与数据库交互之前，Python 的值实际上可能是 None。
如果我们假设 id 总是一个 int，并且没有使用 Optional 添加类型注解，我们可能会写出错误的代码，例如：
next_hero_id = hero_1.id + 1
如果我们在将英雄保存到数据库之前运行这段代码，并且 hero_1.id 仍然是 None，我们会得到如下错误：
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'
但是通过使用 Optional[int] 声明，编辑器会帮助我们避免写出错误的代码，并提醒我们如果 hero_1.id 是 None，代码可能无效。🔍
打印默认的 id 值¶
我们可以通过在将英雄添加到数据库之前打印它们来确认这一点：
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
输出将是：
注意它们的 id=None。
这是我们在 Hero 模型类中定义的默认值。
当我们将这些对象 add 到 session 时会发生什么？
将对象添加到 Session¶
在我们将 Hero 实例对象添加到 session 后，ID 仍然是 None。
我们可以通过使用 with 块创建一个 session，添加对象，然后再次打印它们来验证这一点：
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
# 上方代码省略 👆
def create_heroes():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
这将再次输出对象的 id 为 None：
正如我们之前所见，session 很智能，不会在每次准备更改时都与数据库通信，只有在我们准备好并告诉它 commit 更改时，它才会将所有 SQL 发送到数据库以存储数据。
提交更改到数据库¶
然后我们可以提交 session 中的更改，并再次打印：
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
现在，发生了一些意想不到的事情，看看输出，似乎 Hero 实例对象根本没有数据：
发生的情况是 SQLModel（实际上是 SQLAlchemy）内部将这些对象标记为“过期”，它们 没有最新版本的数据 。这是因为我们可能在数据库中更新了一些字段，例如，假设有一个字段 updated_at: datetime，它在我们保存更改时会自动更新。
同样，其他值也可能发生了变化，因此 session 为了确保安全，会内部将对象标记为过期。
然后，下次我们访问每个属性时，例如：
current_hero_name = hero_1.name
...SQLModel（实际上是 SQLAlchemy）会确保联系数据库并 获取数据的最新版本 ，更新对象中的 name 字段，然后使其对后续的 Python 表达式可用。在上面的例子中，Python 会继续执行，并使用刚刚更新的 hero_1.name 值将其赋值给变量 current_hero_name。
这一切都会自动发生，并且是幕后进行的。✨
而且这是我们示例中的有趣和奇怪之处：
print("Hero 1:", hero_1)
我们并没有访问对象的属性，如 hero.name。我们只是访问了整个对象并打印了它，所以 SQLAlchemy 无法知道 我们想访问该对象的数据。
打印单个字段¶
为了确认和理解当访问属性时如何进行**自动过期和数据刷新**，我们可以打印一些单独的字段（实例属性）：
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
# 下方代码省略 👇
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
现在我们实际上正在访问属性，因为我们不再打印整个对象 hero_1：
print("Hero 1:", hero_1)
...我们现在打印的是 hero.id 中的 id 属性：
print("Hero 1 ID:", hero_1.id)
通过访问属性，这**触发**了 SQLModel（实际上是 SQLAlchemy）在后台进行大量工作，从数据库刷新数据，将其设置到对象的 id 属性中，并使其在 Python 表达式中可用（在本例中就是打印出来）。
让我们看看它是如何工作的：
显式刷新对象¶
你刚刚学习了如何通过 session 在后台自动刷新数据，当你访问某个属性时，数据会作为副作用被刷新。
但是如果你想 显式刷新 数据怎么办呢？
你也可以使用 session.refresh(object) 来做到这一点：
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
当 Python 执行以下代码时：
session.refresh(hero_1)
... session 会让 engine 与数据库进行通信，获取该对象 hero_1 的最新数据，然后将数据放入 hero_1 对象中，并将其标记为“新鲜”或“未过期”。
以下是输出的样子：
这在某些情况下会很有用，例如，如果你正在构建一个用于创建英雄的 Web API。假设一旦创建了某个英雄并保存了一些数据，你将其返回给客户端。
你不希望返回一个看起来空空的对象，因为没有触发自动刷新数据的机制。
在这种情况下，提交对象到数据库后，你可以显式刷新它，然后将其返回给客户端。这将确保对象包含最新的数据。
关闭会话后打印数据¶
现在，作为最后一个实验，我们还可以在 会话 关闭后打印数据。
这里没有什么意外，依然能够正常工作：
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
# 上方代码省略 👆
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
# 下方代码省略 👇
👀 完整文件预览
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
输出再次显示相同的数据：
回顾所有代码¶
现在让我们再次回顾所有的代码。
Tip
每个编号气泡都会显示该行代码在输出中的打印内容。
由于我们在创建**引擎**时使用了 echo=True，我们可以看到在每个步骤中执行的 SQL 语句。
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
from typing import Optional
from sqlmodel import Field, Session, SQLModel, create_engine
class Hero(SQLModel, table=True):
id: Optional[int] = Field(default=None, primary_key=True)
name: str
secret_name: str
age: Optional[int] = None
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():
hero_1 = Hero(name="Deadpond", secret_name="Dive Wilson")
hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")
hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)
print("Before interacting with the database")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
with Session(engine) as session:
session.add(hero_1)
session.add(hero_2)
session.add(hero_3)
print("After adding to the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
session.commit()
print("After committing the session")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After committing the session, show IDs")
print("Hero 1 ID:", hero_1.id)
print("Hero 2 ID:", hero_2.id)
print("Hero 3 ID:", hero_3.id)
print("After committing the session, show names")
print("Hero 1 name:", hero_1.name)
print("Hero 2 name:", hero_2.name)
print("Hero 3 name:", hero_3.name)
session.refresh(hero_1)
session.refresh(hero_2)
session.refresh(hero_3)
print("After refreshing the heroes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
print("After the session closes")
print("Hero 1:", hero_1)
print("Hero 2:", hero_2)
print("Hero 3:", hero_3)
def main():
create_db_and_tables()
create_heroes()
if __name__ == "__main__":
main()
以下是运行该程序时生成的所有输出：
回顾¶
你读完了所有这些内容！真是很多啊！来块蛋糕奖励一下自己吧，你值得拥有。🍰
我们讨论了 会话 如何使用 引擎 向数据库发送 SQL，用于创建数据和获取数据。它如何追踪“ 过期 ”和“ 新鲜 ”的数据。在何时会 自动获取数据 （访问实例属性时）以及如何通过 会话 在内存中的对象和数据库之间同步数据。
如果你理解了这些内容，那么现在你对 SQLModel 、SQLAlchemy，以及 Python 与数据库交互的工作原理有了很深入的了解。
如果你没有完全理解也没关系，随时可以回来 刷新 一下这些概念。refresh
我认为这可能是导致问题和让你头疼的主要错误类型之一。所以，做得好，继续努力学习！💪