app = FastAPI()


@app.get(
    "/items/{item_id}",
    response_model=Item,
    responses={
        200: {
            "content": {"image/png": {}},
            "description": "Return the JSON item or an image.",
        }
    },
)
async def read_item(item_id: str, img: Union[bool, None] = None):
    if img:
        return FileResponse("image.png", media_type="image/png")
    else:

    return {"msg": "Hello World"}


client = TestClient(app)


def test_dependency_set_status_code():
    response = client.get("/")
    assert response.status_code == 201, response.text

    assert '"appName": "The Predendapp"' in response.text
    assert '"clientId": "the-foo-clients"' in response.text


def test_response():
    response = client.get("/items/")

./mc ready myminio

./mc admin user add myminio/ minio123 minio123
./mc admin user add myminio/ minio12345 minio12345

./mc admin policy create myminio/ rw ./docs/distributed/rw.json
./mc admin policy create myminio/ lake ./docs/distributed/rw.json

./mc admin policy attach myminio/ rw --user=minio123
./mc admin policy attach myminio/ lake --user=minio12345

./mc mb -l myminio/versioned

Wenn Sie in Ihrem Browser eine URL wie:

```
http://127.0.0.1:8000/items/foo-item
```

... öffnen, ohne den benötigten Parameter `needy`, dann erhalten Sie einen Fehler wie den folgenden:

```JSON
{
  "detail": [
    {
      "type": "missing",
      "loc": [
        "query",
        "needy"
      ],
      "msg": "Field required",
      "input": null
    }
  ]
}
```

Der beste Ansatz bestand außerdem darin, bereits bestehende Standards zu nutzen.

Bevor ich also überhaupt angefangen habe, **FastAPI** zu schreiben, habe ich mehrere Monate damit verbracht, die Spezifikationen für OpenAPI, JSON Schema, OAuth2, usw. zu studieren und deren Beziehungen, Überschneidungen und Unterschiede zu verstehen.

## Design { #design }

		bugLogIf(GlobalContext, err)
		return nil
	}
	return buf.Bytes()
}

// Encodes the response headers into JSON format.
func encodeResponseJSON(response any) []byte {
	var bytesBuffer bytes.Buffer
	e := json.NewEncoder(&bytesBuffer)
	e.Encode(response)
	return bytesBuffer.Bytes()
}

// Write parts count

It can't handle nested models very well. So, if the JSON body in the request is a JSON object that has inner fields that in turn are nested JSON objects, it cannot be properly documented and validated.

/// check | Inspired **FastAPI** to

Use Python types to have great editor support.

注意，模型属性的类型、默认值及 `Field` 的代码结构与*路径操作函数*的参数相同，只不过是用 `Field` 替换了`Path`、`Query`、`Body`。

///

## 添加更多信息

`Field`、`Query`、`Body` 等对象里可以声明更多信息，并且 JSON Schema 中也会集成这些信息。

*声明示例*一章中将详细介绍添加更多信息的知识。

## 小结

Pydantic 的 `Field` 可以为模型属性声明更多校验和元数据。

    responses={
        404: {"model": Message, "description": "The item was not found"},
        200: {
            "description": "Item requested by ID",
            "content": {
                "application/json": {
                    "example": {"id": "bar", "value": "The bar tenders"}
                }
            },
        },
    },
)
async def read_item(item_id: str):
    if item_id == "foo":