## 什么是服务器发送事件？ { #what-are-server-sent-events }

SSE 是一种通过 HTTP 从服务器向客户端流式传输数据的标准。

每个事件是一个带有 `data`、`event`、`id` 和 `retry` 等“字段”的小文本块，以空行分隔。

看起来像这样：

```
data: {"name": "Portal Gun", "price": 999.99}

data: {"name": "Plumbus", "price": 32.99}

```

SSE 常用于 AI 聊天流式输出、实时通知、日志与可观测性，以及其他服务器向客户端推送更新的场景。

/// tip | 提示

如果你想流式传输二进制数据（例如视频或音频），请查看高级指南：[流式传输数据](../advanced/stream-data.md)。

///

然后我们可以将其用作一个属性的类型：

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

这意味着 **FastAPI** 将期望类似于以下内容的请求体：

```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"
    }
}
```

再一次，仅仅进行这样的声明，你将通过 **FastAPI** 获得：

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

送信するペイロードにも補完が適用されます:

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

/// tip | 豆知識

FastAPI アプリの `Item` モデルで定義した `name` と `price` に補完が効いている点に注目してください。

///

送信データに対するインラインエラーも表示されます:

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

レスポンスオブジェクトにも補完があります:

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

```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):

non-permissive terms added in accord with section 7 apply to the code;
keep intact all notices of the absence of any warranty; and give all
recipients a copy of this License along with the Program.

  You may charge any price or no price for each copy that you convey,
and you may offer support or warranty protection for a fee.

  5. Conveying Modified Source Versions.

  You may convey a work based on the Program, or the modifications to

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

보낼 페이로드에 대해서도 자동 완성이 제공됩니다:

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

/// tip | 팁

`name`과 `price`에 대한 자동 완성은 FastAPI 애플리케이션에서 `Item` 모델에 정의된 내용입니다.

///

전송하는 데이터에 대해 인라인 오류도 표시됩니다:

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

응답 객체도 자동 완성을 제공합니다:

`PUT` 用於接收應該取代現有資料的資料。

### 關於取代的警告 { #warning-about-replacing }

這表示，如果你想用 `PUT` 並在 body 中包含以下內容來更新項目 `bar`：

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

由於這裡沒有包含已儲存的屬性 `"tax": 20.2`，輸入的模型會採用預設值 `"tax": 10.5`。

最終資料會以這個「新的」 `tax` 值 `10.5` 被儲存。

## 使用 `PATCH` 進行部分更新 { #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: str
    description: str | None = None
    price: float = Field(gt=0)


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item, project_id: Annotated[int, Query()]): ...
```

instead of this:

```python
# DO NOT DO THIS
class Item(BaseModel):
    name: str = ...
    description: str | None = None
    price: float = Field(..., gt=0)


app = FastAPI()

### Warning about replacing { #warning-about-replacing }

That means that if you want to update the item `bar` using `PUT` with a body containing:

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

because it doesn't include the already stored attribute `"tax": 20.2`, the input model would take the default value of `"tax": 10.5`.