Nous avions cette annotation de type :

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

Ce que nous allons faire, c’est l’englober avec `Annotated`, de sorte que cela devienne :

```Python
q: Annotated[str | None] = None
```

Les deux versions signifient la même chose, `q` est un paramètre qui peut être une `str` ou `None`, et par défaut, c’est `None`.

Passons maintenant aux choses amusantes. 🎉

    assert response.json() == {
        "detail": [
            {
                "type": "missing",
                "loc": ["body", "p"],
                "msg": "Field required",
                "input": IsOneOf(None, {}),
            }
        ]
    }


@pytest.mark.parametrize(
    "path",
    ["/required-str", "/model-required-str"],
)
def test_required_str(path: str):
    client = TestClient(app)

        "item_id": 5,
        "item": {
            "name": "Foo",
            "price": 50.5,
            "description": None,
            "tax": None,
        },
        "q": "bar",
    }


def test_post_no_body_q_bar(client: TestClient):
    response = client.put("/items/5?q=bar", json=None)
    assert response.status_code == 200
    assert response.json() == {"item_id": 5, "q": "bar"}

ul.has-error {
	color: #dd4b39 !important;
	list-style-type: none;
	padding: 0;
}

.form-group .has-error + .form-control {
	border-color: #dd4b39 !important;
	box-shadow: none;
}

.sidebar-mini.sidebar-collapse .sidebar-search {
	display: none !important;
}

input[type="file"].form-control:not([type="file"]) {
	height: 0% !important;
}

#result ol {
	list-style: none !important;
	padding-left: 0;
}

在這種情況下（未使用 `Annotated`），我們必須用 `Query()` 取代函式中的預設值 `None`，因此需要用 `Query(default=None)` 來設定預設值；對 FastAPI 而言，這達到相同目的。

所以：

```Python
q: str | None = Query(default=None)
```

…會讓參數變為可選、預設值是 `None`，等同於：

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

但用 `Query` 的版本會明確宣告它是查詢參數。

接著，我們可以傳更多參數給 `Query`。此例中是用於字串的 `max_length` 參數：

```Python
q: str | None = Query(default=None, max_length=50)
```

   ...

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 = Path(title="The ID of the item to get", ge=0, le=1000),
    q: str | None = None,
    item: Item | None = None,
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

    assert response.json() == {
        "detail": [
            {
                "type": "missing",
                "loc": ["body", "p"],
                "msg": "Field required",
                "input": None,
            }
        ]
    }


@pytest.mark.parametrize(
    "path",
    [
        "/list-bytes",
        "/list-uploadfile",
    ],
)
def test_list(path: str):

from sqlmodel import Field, Session, SQLModel, create_engine, select


class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    age: int | None = Field(default=None, index=True)
    secret_name: str


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

app = FastAPI()


@app.post("/urlencoded")
async def post_url_encoded(age: Annotated[int | None, Form()] = None):
    return age


@app.post("/multipart")
async def post_multi_part(
    age: Annotated[int | None, Form()] = None,
    file: Annotated[bytes | None, File()] = None,
):
    return {"file": file, "age": age}


client = TestClient(app)


def test_form_default_url_encoded():