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)：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

在与数据库交互之前
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

添加到 session 后
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

// 这里是引擎与数据库交互的部分，SQL 操作
INFO Engine BEGIN (implicit)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [generated in 0.00018s] ('Deadpond', 'Dive Wilson', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.0008968s ago] ('Spider-Boy', 'Pedro Parqueador', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.001143s ago] ('Rusty-Man', 'Tommy Sharp', 48)
INFO Engine COMMIT

// 现在是我们的打印输出
提交 session 后
Hero 1:
Hero 2:
Hero 3:

// 这里发生了什么？😱

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）：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

// 提交后，对象已过期且没有值
提交 session 后
Hero 1:
Hero 2:
Hero 3:

// 现在我们将访问像 ID 这样的属性，这是第一次打印
提交 session 后，显示 ID

// 请注意，在打印第一个 ID 之前，Session 会让 Engine 去数据库刷新数据 🤓
INFO Engine BEGIN (implicit)
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
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00017s] (1,)

// 这是我们的第一次打印，现在我们有了数据库生成的 ID
Hero 1 ID: 1

// 在打印下一个 ID 之前，刷新第二个对象的数据
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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001245s ago] (2,)

// 这是我们的第二个英雄打印，带有自动生成的 ID
Hero 2 ID: 2

// 在第三个打印之前，刷新它的数据
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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002215s ago] (3,)

// 这是我们的第三个英雄打印
Hero 3 ID: 3

// 如果我们打印另一个属性，比如名字呢？
提交 session 后，显示名字
Hero 1 name: Deadpond
Hero 2 name: Spider-Boy
Hero 3 name: Rusty-Man

// 因为 Session 已经刷新了这些对象的所有数据，并且 Session 知道它们没有过期，所以它不需要再次去数据库获取名字 🤓

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

// 第一次刷新
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00024s] (1,)

// 第二次刷新
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001487s ago] (2,)

// 第三次刷新
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002377s ago] (3,)

// 现在打印数据，由于数据已经刷新，Session 不需要再次刷新
刷新英雄后
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'

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：

Python 3.10+Python 3.7+

# 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

Python 3.10+Python 3.7+

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：

$ python app.py

// 上方输出省略 👆

// 在完成 with 块后，会话已关闭，包括任何未提交的挂起事务的回滚
INFO Engine ROLLBACK

// 然后我们打印数据，正常工作
会话关闭后
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'

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。

Python 3.10+Python 3.7+

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")  # (1)!
    hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")  # (2)!
    hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)  # (3)!

    print("Before interacting with the database")  # (4)!
    print("Hero 1:", hero_1)  # (5)!
    print("Hero 2:", hero_2)  # (6)!
    print("Hero 3:", hero_3)  # (7)!

    with Session(engine) as session:  # (8)!
        session.add(hero_1)  # (9)!
        session.add(hero_2)  # (10)!
        session.add(hero_3)  # (11)!

        print("After adding to the session")  # (12)!
        print("Hero 1:", hero_1)  # (13)!
        print("Hero 2:", hero_2)  # (14)!
        print("Hero 3:", hero_3)  # (15)!

        session.commit()  # (16)!

        print("After committing the session")  # (17)!
        print("Hero 1:", hero_1)  # (18)!
        print("Hero 2:", hero_2)  # (19)!
        print("Hero 3:", hero_3)  # (20)!

        print("After committing the session, show IDs")  # (21)!
        print("Hero 1 ID:", hero_1.id)  # (22)!
        print("Hero 2 ID:", hero_2.id)  # (23)!
        print("Hero 3 ID:", hero_3.id)  # (24)!

        print("After committing the session, show names")  # (25)!
        print("Hero 1 name:", hero_1.name)  # (26)!
        print("Hero 2 name:", hero_2.name)  # (27)!
        print("Hero 3 name:", hero_3.name)  # (28)!

        session.refresh(hero_1)  # (29)!
        session.refresh(hero_2)  # (30)!
        session.refresh(hero_3)  # (31)!

        print("After refreshing the heroes")  # (32)!
        print("Hero 1:", hero_1)  # (33)!
        print("Hero 2:", hero_2)  # (34)!
        print("Hero 3:", hero_3)  # (35)!
    # (36)!

    print("After the session closes")  # (37)!
    print("Hero 1:", hero_1)  # (38)!
    print("Hero 2:", hero_2)  # (39)!
    print("Hero 3:", hero_3)  # (40)!


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

Create the hero_1.

Doesn't generate any output.
Create the hero_2.

Doesn't generate any output.
Create the hero_3.

Doesn't generate any output.
Print the line "Before interacting with the database".

Generates the output:
```
Before interacting with the database
```
Print the hero_1 before interacting with the database.

Generates the output:
```
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
```

Print the hero_2 before interacting with the database.

Generates the output:

Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None

Print the hero_3 before interacting with the database.

Generates the output:
```
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
```
Create the Session in a with block.

Doesn't generate any output.
Add the hero_1 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Add the hero_2 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Add the hero_3 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Print the line "After adding to the session".

Generates the output:
```
After adding to the session
```
Print the hero_1 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
```
Print the hero_2 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
```
Print the hero_3 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
```

commit the session.

This will save all the data to the database. The session will use the engine to run a lot of SQL.

Generates the output:

INFO Engine BEGIN (implicit)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [generated in 0.00018s] ('Deadpond', 'Dive Wilson', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.0008968s ago] ('Spider-Boy', 'Pedro Parqueador', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.001143s ago] ('Rusty-Man', 'Tommy Sharp', 48)
INFO Engine COMMIT

Print the line "After committing the session".

Generates the output:
```
After committing the session
```
Print the hero_1 after committing the session.

The hero_1 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 1:
```
Print the hero_2 after committing the session.

The hero_2 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 2:
```
Print the hero_3 after committing the session.

The hero_3 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 3:
```
Print the line "After committing the session, show IDs".

Generates the output:
```
After committing the session, show IDs
```
Print the hero_1.id. A lot happens here.

Because we are accessing the attribute id of hero_1, SQLModel (actually SQLAlchemy) can detect that we are trying to access data from the hero_1.

It then detects that hero_1 is currently associated with a session (because we added it to the session and committed it), and it is marked as expired.

Then with the session, it uses the engine to execute all the SQL to fetch the data for this object from the database.

Next it updates the object with the new data and marks it internally as "fresh" or "not expired".

Finally, it makes the ID value available for the rest of the Python expression. In this case, the Python expression just prints the ID.

Generates the output:
```
INFO Engine BEGIN (implicit)
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
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00017s] (1,)

Hero 1 ID: 1
```

Print the hero_2.id.

A lot happens here, all the same stuff that happened at point 22, but for this hero_2 object.

Generates the output:

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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001245s ago] (2,)

Hero 2 ID: 2

Print the hero_3.id.

A lot happens here, all the same stuff that happened at point 22, but for this hero_3 object.

Generates the output:

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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002215s ago] (3,)


Hero 3 ID: 3

Print the line "After committing the session, show names".

Generates the output:
```
After committing the session, show names
```
Print the hero_1.name.

Because hero_1 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 1 name: Deadpond
```
Print the hero_2.name.

Because hero_2 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 2 name: Spider-Boy
```
Print the hero_3.name.

Because hero_3 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 3 name: Rusty-Man
```
Explicitly refresh the hero_1 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_1 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00024s] (1,)
```
Explicitly refresh the hero_2 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_2 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001487s ago] (2,)
```
Explicitly refresh the hero_3 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_3 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002377s ago] (3,)
```
Print the line "After refreshing the heroes".

Generates the output:
```
After refreshing the heroes
```
Print the hero_1.

Info

Even if the hero_1 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_1 is fresh it has all it's data available.

Generates the output:
```
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
```
Print the hero_2.

Info

Even if the hero_2 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_2 is fresh it has all it's data available.

Generates the output:
```
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
```
Print the hero_3.

Info

Even if the hero_3 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_3 is fresh it has all it's data available.

Generates the output:
```
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'
```
The with block ends here (there's no more indented code), so the session is closed, running all it's closing code.

This includes doing a ROLLBACK of any possible transaction that could have been started.

Generates the output:
```
INFO Engine ROLLBACK
```
Print the line "After the session closes".

Generates the output:
```
After the session closes
```

Print the hero_1 after closing the session.

Generates the output:

Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'

Print the hero_2 after closing the session.

Generates the output:

Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'

Print the hero_3 after closing the session.

Generates the output:

Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'

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")  # (1)!
    hero_2 = Hero(name="Spider-Boy", secret_name="Pedro Parqueador")  # (2)!
    hero_3 = Hero(name="Rusty-Man", secret_name="Tommy Sharp", age=48)  # (3)!

    print("Before interacting with the database")  # (4)!
    print("Hero 1:", hero_1)  # (5)!
    print("Hero 2:", hero_2)  # (6)!
    print("Hero 3:", hero_3)  # (7)!

    with Session(engine) as session:  # (8)!
        session.add(hero_1)  # (9)!
        session.add(hero_2)  # (10)!
        session.add(hero_3)  # (11)!

        print("After adding to the session")  # (12)!
        print("Hero 1:", hero_1)  # (13)!
        print("Hero 2:", hero_2)  # (14)!
        print("Hero 3:", hero_3)  # (15)!

        session.commit()  # (16)!

        print("After committing the session")  # (17)!
        print("Hero 1:", hero_1)  # (18)!
        print("Hero 2:", hero_2)  # (19)!
        print("Hero 3:", hero_3)  # (20)!

        print("After committing the session, show IDs")  # (21)!
        print("Hero 1 ID:", hero_1.id)  # (22)!
        print("Hero 2 ID:", hero_2.id)  # (23)!
        print("Hero 3 ID:", hero_3.id)  # (24)!

        print("After committing the session, show names")  # (25)!
        print("Hero 1 name:", hero_1.name)  # (26)!
        print("Hero 2 name:", hero_2.name)  # (27)!
        print("Hero 3 name:", hero_3.name)  # (28)!

        session.refresh(hero_1)  # (29)!
        session.refresh(hero_2)  # (30)!
        session.refresh(hero_3)  # (31)!

        print("After refreshing the heroes")  # (32)!
        print("Hero 1:", hero_1)  # (33)!
        print("Hero 2:", hero_2)  # (34)!
        print("Hero 3:", hero_3)  # (35)!
    # (36)!

    print("After the session closes")  # (37)!
    print("Hero 1:", hero_1)  # (38)!
    print("Hero 2:", hero_2)  # (39)!
    print("Hero 3:", hero_3)  # (40)!


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

Create the hero_1.

Doesn't generate any output.
Create the hero_2.

Doesn't generate any output.
Create the hero_3.

Doesn't generate any output.
Print the line "Before interacting with the database".

Generates the output:
```
Before interacting with the database
```
Print the hero_1 before interacting with the database.

Generates the output:
```
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
```

Print the hero_2 before interacting with the database.

Generates the output:

Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None

Print the hero_3 before interacting with the database.

Generates the output:
```
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
```
Create the Session in a with block.

Doesn't generate any output.
Add the hero_1 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Add the hero_2 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Add the hero_3 to the session.

This still doesn't save it to the database.

Doesn't generate any output.
Print the line "After adding to the session".

Generates the output:
```
After adding to the session
```
Print the hero_1 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
```
Print the hero_2 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
```
Print the hero_3 after adding it to the session.

It still has the same data as there hasn't been any interaction with the database yet. Notice that the id is still None.

Generates the output:
```
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
```

commit the session.

This will save all the data to the database. The session will use the engine to run a lot of SQL.

Generates the output:

INFO Engine BEGIN (implicit)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [generated in 0.00018s] ('Deadpond', 'Dive Wilson', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.0008968s ago] ('Spider-Boy', 'Pedro Parqueador', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.001143s ago] ('Rusty-Man', 'Tommy Sharp', 48)
INFO Engine COMMIT

Print the line "After committing the session".

Generates the output:
```
After committing the session
```
Print the hero_1 after committing the session.

The hero_1 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 1:
```
Print the hero_2 after committing the session.

The hero_2 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 2:
```
Print the hero_3 after committing the session.

The hero_3 is now internally marked as expired, and until it is refreshed, it looks like if it didn't contain any data.

Generates the output:
```
Hero 3:
```
Print the line "After committing the session, show IDs".

Generates the output:
```
After committing the session, show IDs
```
Print the hero_1.id. A lot happens here.

Because we are accessing the attribute id of hero_1, SQLModel (actually SQLAlchemy) can detect that we are trying to access data from the hero_1.

It then detects that hero_1 is currently associated with a session (because we added it to the session and committed it), and it is marked as expired.

Then with the session, it uses the engine to execute all the SQL to fetch the data for this object from the database.

Next it updates the object with the new data and marks it internally as "fresh" or "not expired".

Finally, it makes the ID value available for the rest of the Python expression. In this case, the Python expression just prints the ID.

Generates the output:
```
INFO Engine BEGIN (implicit)
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
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00017s] (1,)

Hero 1 ID: 1
```

Print the hero_2.id.

A lot happens here, all the same stuff that happened at point 22, but for this hero_2 object.

Generates the output:

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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001245s ago] (2,)

Hero 2 ID: 2

Print the hero_3.id.

A lot happens here, all the same stuff that happened at point 22, but for this hero_3 object.

Generates the output:

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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002215s ago] (3,)


Hero 3 ID: 3

Print the line "After committing the session, show names".

Generates the output:
```
After committing the session, show names
```
Print the hero_1.name.

Because hero_1 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 1 name: Deadpond
```
Print the hero_2.name.

Because hero_2 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 2 name: Spider-Boy
```
Print the hero_3.name.

Because hero_3 is still fresh, no additional data is fetched, no additional SQL is executed, and the name is available.

Generates the output:
```
Hero 3 name: Rusty-Man
```
Explicitly refresh the hero_1 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_1 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00024s] (1,)
```
Explicitly refresh the hero_2 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_2 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001487s ago] (2,)
```
Explicitly refresh the hero_3 object.

The session will use the engine to execute the SQL necessary to fetch fresh data from the database for the hero_3 object.

Generates the output:
```
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002377s ago] (3,)
```
Print the line "After refreshing the heroes".

Generates the output:
```
After refreshing the heroes
```
Print the hero_1.

Info

Even if the hero_1 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_1 is fresh it has all it's data available.

Generates the output:
```
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
```
Print the hero_2.

Info

Even if the hero_2 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_2 is fresh it has all it's data available.

Generates the output:
```
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
```
Print the hero_3.

Info

Even if the hero_3 wasn't fresh, this would not trigger a refresh making the session use the engine to fetch data from the database because it is not accessing an attribute.

Because the hero_3 is fresh it has all it's data available.

Generates the output:
```
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'
```
The with block ends here (there's no more indented code), so the session is closed, running all it's closing code.

This includes doing a ROLLBACK of any possible transaction that could have been started.

Generates the output:
```
INFO Engine ROLLBACK
```
Print the line "After the session closes".

Generates the output:
```
After the session closes
```

Print the hero_1 after closing the session.

Generates the output:

Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'

Print the hero_2 after closing the session.

Generates the output:

Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'

Print the hero_3 after closing the session.

Generates the output:

Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'

以下是运行该程序时生成的所有输出：

$ python app.py

INFO Engine BEGIN (implicit)
INFO Engine PRAGMA main.table_info("hero")
INFO Engine [raw sql] ()
INFO Engine PRAGMA temp.table_info("hero")
INFO Engine [raw sql] ()
INFO Engine
CREATE TABLE hero (
        id INTEGER,
        name VARCHAR NOT NULL,
        secret_name VARCHAR NOT NULL,
        age INTEGER,
        PRIMARY KEY (id)
)


INFO Engine [no key 0.00018s] ()
INFO Engine COMMIT
Before interacting with the database
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
After adding to the session
Hero 1: id=None name='Deadpond' secret_name='Dive Wilson' age=None
Hero 2: id=None name='Spider-Boy' secret_name='Pedro Parqueador' age=None
Hero 3: id=None name='Rusty-Man' secret_name='Tommy Sharp' age=48
INFO Engine BEGIN (implicit)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [generated in 0.00022s] ('Deadpond', 'Dive Wilson', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.001127s ago] ('Spider-Boy', 'Pedro Parqueador', None)
INFO Engine INSERT INTO hero (name, secret_name, age) VALUES (?, ?, ?)
INFO Engine [cached since 0.001483s ago] ('Rusty-Man', 'Tommy Sharp', 48)
INFO Engine COMMIT
After committing the session
Hero 1:
Hero 2:
Hero 3:
After committing the session, show IDs
INFO Engine BEGIN (implicit)
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
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00029s] (1,)
Hero 1 ID: 1
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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002132s ago] (2,)
Hero 2 ID: 2
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
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.003367s ago] (3,)
Hero 3 ID: 3
After committing the session, show names
Hero 1 name: Deadpond
Hero 2 name: Spider-Boy
Hero 3 name: Rusty-Man
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [generated in 0.00025s] (1,)
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.001583s ago] (2,)
INFO Engine SELECT hero.id, hero.name, hero.secret_name, hero.age
FROM hero
WHERE hero.id = ?
INFO Engine [cached since 0.002722s ago] (3,)
After refreshing the heroes
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'
INFO Engine ROLLBACK
After the session closes
Hero 1: age=None id=1 name='Deadpond' secret_name='Dive Wilson'
Hero 2: age=None id=2 name='Spider-Boy' secret_name='Pedro Parqueador'
Hero 3: age=48 id=3 name='Rusty-Man' secret_name='Tommy Sharp'

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！💪

自动生成的 ID、None 默认值和数据刷新¶

创建一个新的 Hero 实例¶

Optional 如何帮助¶

打印默认的 id 值¶

将对象添加到 Session¶

提交更改到数据库¶

打印单个字段¶

显式刷新对象¶

关闭会话后打印数据¶

回顾所有代码¶

回顾¶

自动生成的 ID、`None` 默认值和数据刷新¶

创建一个新的 `Hero` 实例¶

`Optional` 如何帮助¶

打印默认的 `id` 值¶