*
 * <p>This class should not be assumed to be universally superior to {@code
 * java.util.LinkedHashMap}. Generally speaking, this class reduces object allocation and memory
 * consumption at the price of moderately increased constant factors of CPU. Only use this class
 * when there is a specific reason to prioritize memory over CPU.
 *
 * @author Louis Wasserman
 */

借助 Pydantic，使用标准的 Python 类型来声明请求体。

```Python hl_lines="2  7-10 23-25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):

现在你可以导入并使用客户端代码了。它可能是这样，并且你会发现方法有自动补全：

<img src="/img/tutorial/generate-clients/image02.png">

要发送的载荷也会有自动补全：

<img src="/img/tutorial/generate-clients/image03.png">

/// tip | 提示

请注意 `name` 和 `price` 的自动补全，它们是在 FastAPI 应用中的 `Item` 模型里定义的。

///

你发送的数据如果不符合要求，会在编辑器中显示内联错误：

<img src="/img/tutorial/generate-clients/image04.png">

响应对象同样有自动补全：

<img src="/img/tutorial/generate-clients/image05.png">

そして、それを属性の型として使用することができます:

{* ../../docs_src/body_nested_models/tutorial004_py310.py hl[18] *}

これは **FastAPI** が以下のようなボディを期待することを意味します:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

{* ../../docs_src/body_updates/tutorial001_py310.py hl[28:33] *}

`PUT` 用于接收替换现有数据的数据。

### 关于替换的警告 { #warning-about-replacing }

用 `PUT` 把数据项 `bar` 更新为以下请求体时：

```Python
{
    "name": "Barz",
    "price": 3,
    "description": None,
}
```

因为其中未包含已存储的属性 `"tax": 20.2`，输入模型会取 `"tax": 10.5` 的默认值。

因此，保存的数据会带有这个“新的” `tax` 值 `10.5`。

## 用 `PATCH` 进行部分更新 { #partial-updates-with-patch }

```Python hl_lines="2  7-10 23-25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):

{
    "name": "Bar",
    "description": "The bartenders",
    "price": 62,
    "tax": 20.2
}
```

它們會被包含在回應中。

#### 與預設值相同的資料 { #data-with-the-same-values-as-the-defaults }

如果資料的值與預設值相同，例如 ID 為 `baz` 的項目：

```Python hl_lines="3  5-6"
{
    "name": "Baz",
    "description": None,
    "price": 50.2,
    "tax": 10.5,
    "tags": []
}
```

```Python hl_lines="2  7-10 23-25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):

```Python hl_lines="2  7-10 23-25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):

```Python hl_lines="2  7-10 23-25"
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):