* If it is not, the client will see a useful, clear error.
* Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests.
    * As the `q` parameter is declared with `= None`, it is optional.
    * Without the `None` it would be required (as is the body in the case with `PUT`).

## First dependency "dependable" { #first-dependency-dependable }

You could create a first dependency ("dependable") like:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

It declares an optional query parameter `q` as a `str`, and then it just returns it.

This is quite simple (not very useful), but will help us focus on how the sub-dependencies work.

from typing import Optional

import pytest
from dirty_equals import HasRepr
from fastapi import Depends, FastAPI
from fastapi.exceptions import ResponseValidationError
from fastapi.testclient import TestClient
from inline_snapshot import snapshot


@pytest.fixture(name="client")
def get_client():
    from pydantic import BaseModel, ValidationInfo, field_validator

    app = FastAPI()

    class ModelB(BaseModel):

import org.codelibs.fess.opensearch.config.exentity.WebAuthentication;
import org.codelibs.fess.util.ParameterUtil;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.optional.OptionalEntity;

import jakarta.annotation.Resource;

/**
 * Service class for managing web authentication configurations.
 * Provides CRUD operations for web authentication settings including

# Optional Path parameters are not supported...

import static java.lang.reflect.Modifier.PRIVATE;
import static java.lang.reflect.Modifier.PROTECTED;
import static java.lang.reflect.Modifier.PUBLIC;
import static java.util.Arrays.asList;

import com.google.common.base.Optional;
import com.google.common.reflect.ClassPath;
import com.google.common.reflect.ClassPath.ClassInfo;
import com.google.common.reflect.TypeToken;
import java.lang.reflect.Method;
import junit.framework.TestCase;

import org.codelibs.fess.opensearch.config.exbhv.RoleTypeBhv;
import org.codelibs.fess.opensearch.config.exentity.RoleType;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.optional.OptionalEntity;

import jakarta.annotation.Resource;

/**
 * Service class for managing role types.
 */
public class RoleTypeService {

    /**
     * Constructor.
     */

import org.codelibs.fess.opensearch.config.exentity.ElevateWord;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;

 * under the License.
 */
package org.apache.maven.cling.invoker;

import java.nio.file.Path;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.Properties;
import java.util.ServiceLoader;
import java.util.function.UnaryOperator;

import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.annotations.Nullable;

以下のアプリケーションを例にしてみましょう:

{* ../../docs_src/query_params_str_validations/tutorial001.py hl[9] *}

クエリパラメータ `q` は `Optional[str]` 型で、`None` を許容する `str` 型を意味しており、デフォルトは `None` です。そのため、FastAPIはそれが必須ではないと理解します。

/// note | 備考

FastAPIは、 `q` はデフォルト値が `=None` であるため、必須ではないと理解します。

`Optional[str]` における `Optional` はFastAPIには利用されませんが、エディターによるより良いサポートとエラー検出を可能にします。

///

## バリデーションの追加