alias=alias,
            title=title,
            description=description,
            gt=gt,
            ge=ge,
            lt=lt,
            le=le,
            min_length=min_length,
            max_length=max_length,
            discriminator=discriminator,
            multiple_of=multiple_of,
            allow_inf_nan=allow_inf_nan,
            max_digits=max_digits,
            decimal_places=decimal_places,

        serialization_alias=serialization_alias,
        title=title,
        description=description,
        gt=gt,
        ge=ge,
        lt=lt,
        le=le,
        min_length=min_length,
        max_length=max_length,
        pattern=pattern,
        regex=regex,
        discriminator=discriminator,
        strict=strict,
        multiple_of=multiple_of,
        allow_inf_nan=allow_inf_nan,

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

@app.get("/path/param-minlength/{item_id}")
def get_path_param_min_length(item_id: str = Path(min_length=3)):
    return item_id


@app.get("/path/param-maxlength/{item_id}")
def get_path_param_max_length(item_id: str = Path(max_length=3)):
    return item_id


@app.get("/path/param-min_maxlength/{item_id}")
def get_path_param_min_max_length(item_id: str = Path(max_length=3, min_length=2)):
    return item_id


@app.get("/path/param-gt/{item_id}")

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

{* ../../docs_src/query_params_str_validations/tutorial002_an_py310.py hl[9] *}

Notice that the default value is still `None`, so the parameter is still optional.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(default=None, min_length=3, max_length=50),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

        default=None,
        alias="item-query",
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
        max_length=50,
        pattern="^fixedquery$",
        deprecated=True,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

            {
                "type": "string_too_long",
                "loc": ["query", "q"],
                "msg": "String should have at most 50 characters",
                "input": "q" * 51,
                "ctx": {"max_length": 50},
            }
        ]
    }


def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text