/// note

FastAPI will know that the value of `q` is not required because of the default value `= None`.

The `str | None` (Python 3.10+) or `Union` in `Union[str, None]` (Python 3.9+) is not used by FastAPI to determine that the value is not required, it will know it's not required because it has a default value of `= None`.

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package csv

import (
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"strings"
	"unicode/utf8"
)

const (
	none   = "none"
	use    = "use"
	ignore = "ignore"

	defaultRecordDelimiter      = "\n"
	defaultFieldDelimiter       = ","
	defaultQuoteCharacter       = `"`
	defaultQuoteEscapeCharacter = `"`

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

Because of that, the JSON Schema for a model can be different depending on if it's used for **input or output**:

* for **input** the `description` will **not be required**
* for **output** it will be **required** (and possibly `None`, or in JSON terms, `null`)

    "path,expected_status,expected_response",
    [
        ("/items", 200, {"q": None, "skip": 0, "limit": 100}),
        ("/items?q=foo", 200, {"q": "foo", "skip": 0, "limit": 100}),
        ("/items?q=foo&skip=5", 200, {"q": "foo", "skip": 5, "limit": 100}),
        ("/items?q=foo&skip=5&limit=30", 200, {"q": "foo", "skip": 5, "limit": 30}),
        ("/users", 200, {"q": None, "skip": 0, "limit": 100}),
    ],
)

from typing import Union

from fastapi import APIRouter, FastAPI
from pydantic import BaseModel, HttpUrl

app = FastAPI()


class Invoice(BaseModel):
    id: str
    title: Union[str, None] = None
    customer: str
    total: float


class InvoiceEvent(BaseModel):
    description: str
    paid: bool


class InvoiceEventReceived(BaseModel):
    ok: bool


invoices_callback_router = APIRouter()

    assert response.json() == {
        "detail": [
            {
                "type": "missing",
                "loc": ["cookie", "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)

def get_client():
    app = FastAPI()
    with pytest.warns(FastAPIDeprecationWarning):

        @app.get("/items/")
        async def read_items(
            q: Annotated[str | None, Query(regex="^fixedquery$")] = None,
        ):
            if q:
                return f"Hello {q}"
            else:
                return "Hello World"

    client = TestClient(app)
    return client


@needs_py310

class DummyClient:
    async def get_people(self) -> list:
        return ["John Doe", "Jane Doe"]

    async def close(self) -> None:
        pass


async def get_client() -> AsyncGenerator[DummyClient, None]:
    client = DummyClient()
    yield client
    await client.close()


Client = Annotated[DummyClient, Depends(get_client)]


@pytest.fixture(name="client")

class Session:
    def __init__(self) -> None:
        self.data = ["foo", "bar", "baz"]
        self.open = True

    def __iter__(self) -> Generator[str, None, None]:
        for item in self.data:
            if self.open:
                yield item
            else:
                raise ValueError("Session closed")


@contextmanager
def acquire_session() -> Generator[Session, None, None]:
    session = Session()
    try:

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


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