from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "sqlite:///./sql_app.db"
# SQLALCHEMY_DATABASE_URL = "postgresql://user:password@postgresserver/db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "sqlite:///./sql_app.db"
# SQLALCHEMY_DATABASE_URL = "postgresql://user:password@postgresserver/db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from ..database import Base
from ..main import app, get_db

SQLALCHEMY_DATABASE_URL = "sqlite:///./test.db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)
TestingSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)


Base.metadata.create_all(bind=engine)

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from ..database import Base
from ..main import app, get_db

SQLALCHEMY_DATABASE_URL = "sqlite:///./test.db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)
TestingSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)


Base.metadata.create_all(bind=engine)

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "sqlite:///./sql_app.db"
# SQLALCHEMY_DATABASE_URL = "postgresql://user:password@postgresserver/db"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.pool import StaticPool

from ..database import Base
from ..main import app, get_db

SQLALCHEMY_DATABASE_URL = "sqlite://"

engine = create_engine(
    SQLALCHEMY_DATABASE_URL,
    connect_args={"check_same_thread": False},
    poolclass=StaticPool,
)
TestingSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

每个实例`SessionLocal`都会是一个数据库会话。当然该类本身还不是数据库会话。

但是一旦我们创建了一个`SessionLocal`类的实例，这个实例将是实际的数据库会话。

我们命名它是`SessionLocal`为了将它与我们从 SQLAlchemy 导入的`Session`区别开来。

稍后我们将使用`Session`（从 SQLAlchemy 导入的那个）。

要创建`SessionLocal`类，请使用函数`sessionmaker`：

```Python hl_lines="11"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### 创建一个`Base`类

现在我们将使用`declarative_base()`返回一个类。

稍后我们将用这个类继承，来创建每个数据库模型或类（ORM 模型）：

We name it `SessionLocal` to distinguish it from the `Session` we are importing from SQLAlchemy.

We will use `Session` (the one imported from SQLAlchemy) later.

To create the `SessionLocal` class, use the function `sessionmaker`:

```Python hl_lines="11"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### Create a `Base` class

Now we will use the function `declarative_base()` that returns a class.

✋️ 🕐 👥 ✍ 👐 `SessionLocal` 🎓, 👉 👐 🔜 ☑ 💽 🎉.

👥 📛 ⚫️ `SessionLocal` 🔬 ⚫️ ⚪️➡️ `Session` 👥 🏭 ⚪️➡️ 🇸🇲.

👥 🔜 ⚙️ `Session` (1️⃣ 🗄 ⚪️➡️ 🇸🇲) ⏪.

✍ `SessionLocal` 🎓, ⚙️ 🔢 `sessionmaker`:

```Python hl_lines="11"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### ✍ `Base` 🎓

🔜 👥 🔜 ⚙️ 🔢 `declarative_base()` 👈 📨 🎓.