</mxCell>
                <mxCell id="3" value="&lt;font face=&quot;Roboto&quot;&gt;&lt;span style=&quot;font-size: 24px&quot;&gt;Server&lt;/span&gt;&lt;/font&gt;" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;strokeWidth=3;fontFamily=Roboto Mono, mono;FType=g;" parent="1" vertex="1">
                    <mxGeometry x="755" y="290" width="300" height="80" as="geometry"/>

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Item = Body(
        openapi_examples={
            "normal": {
                "summary": "A normal example",

from typing import Union

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Item = Body(
        openapi_examples={
            "normal": {

```

由于我们必须用 `Query(default=None)` 替换默认值 `None`，`Query` 的第一个参数同样也是用于定义默认值。

所以：

```Python
q: Union[str, None] = Query(default=None)
```

...使得参数可选，等同于：

```Python
q: str = None
```

但是 `Query` 显式地将其声明为查询参数。

然后，我们可以将更多的参数传递给 `Query`。在本例中，适用于字符串的 `max_length` 参数：

```Python
q: Union[str, None] = Query(default=None, max_length=50)
```

      "gridPos": {
        "h": 4,
        "w": 8,
        "x": 0,
        "y": 4
      },
      "id": 12,
      "links": [],
      "maxDataPoints": 100,
      "options": {
        "colorMode": "none",
        "graphMode": "area",
        "justifyMode": "auto",
        "orientation": "horizontal",
        "reduceOptions": {
          "calcs": [
            "lastNotNull"
          ],

   *
   * <p>Duplicate elements are considered equal. For example, the list [1, 1] will have only one
   * permutation, instead of two. This is why the elements have to implement {@link Comparable}.
   *
   * <p>An empty iterable has only one permutation, which is an empty list.
   *
   * <p>This method is equivalent to {@code Collections2.orderedPermutations(list,
   * Ordering.natural())}.

        }

        String s = stripBasedirToken(path);

        File file = new File(s);
        if (file.isAbsolute()) {
            // path was already absolute, just normalize file separator and we're done
            s = file.getPath();
        } else if (file.getPath().startsWith(File.separator)) {
            // drive-relative Windows path, don't align with project directory but with drive root

## Retrying Requests

Sometimes connections fail: either a pooled connection was stale and disconnected, or the webserver itself couldn’t be reached. OkHttp will retry the request with a different route if one is available.

   */
  private val tcpConnectsInFlight = CopyOnWriteArrayList<Plan>()

  /**
   * Results are posted here as they occur. The find job is done when either one plan completes
   * successfully or all plans fail.
   */
  private val connectResults = taskRunner.backend.decorate(LinkedBlockingDeque<ConnectResult>())

  override fun find(): RealConnection {

    client = TestClient(app)
    return client


def test_create_item(client: TestClient) -> None:
    response = client.post("/items/", json={"name": "Foo"})
    assert response.status_code == 200, response.text
    assert response.json() == {"name": "Foo", "description": None}


def test_read_items(client: TestClient) -> None:
    response = client.get("/items/")
    assert response.status_code == 200, response.text