```Python hl_lines="1  3"
    {!> ../../../docs_src/path_params_numeric_validations/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="1  3"
    {!> ../../../docs_src/path_params_numeric_validations/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="3-4"
    {!> ../../../docs_src/path_params_numeric_validations/tutorial001_an.py!}
    ```

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an.py!}
    ```

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_an.py!}
    ```

# 查询参数和字符串校验

**FastAPI** 允许你为参数声明额外的信息和校验。

让我们以下面的应用程序为例：

=== "Python 3.10+"

    ```Python hl_lines="7"
    {!> ../../../docs_src/query_params_str_validations/tutorial001_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params_str_validations/tutorial001.py!}
    ```

查询参数 `q` 的类型为 `str`，默认值为 `None`，因此它是可选的。

## 额外的校验

    visited.append(dependant.cache_key)

    flat_dependant = Dependant(
        path_params=dependant.path_params.copy(),
        query_params=dependant.query_params.copy(),
        header_params=dependant.header_params.copy(),
        cookie_params=dependant.cookie_params.copy(),
        body_params=dependant.body_params.copy(),
        security_schemes=dependant.security_requirements.copy(),

                  .onResultOf((List<Class<?>> params) -> params.contains(Throwable.class)))
          .reverse();
  private static final Ordering<Constructor<?>> WITH_STRING_PARAM_THEN_WITH_THROWABLE_PARAM =
      ORDERING_BY_CONSTRUCTOR_PARAMETER_LIST.onResultOf(
          constructor -> asList(constructor.getParameterTypes()));

  @CheckForNull
  private static <X> X newFromConstructor(Constructor<X> constructor, Throwable cause) {

            request.setAttribute(Constants.REQUEST_QUERIES, params.getQuery());
        });

        String query = ComponentUtil.getQueryStringBuilder().params(params).sortField(params.getSort()).build();
        List<Map<String, Object>> documentItems;
        try {
            documentItems = searchInternal(query, params, userBean);

@needs_py39
def test_query_params_str_validations_item_query_fixedquery(client: TestClient):
    response = client.get("/items/", params={"item-query": "fixedquery"})
    assert response.status_code == 200
    assert response.json() == {
        "items": [{"item_id": "Foo"}, {"item_id": "Bar"}],
        "q": "fixedquery",
    }


@needs_py39
def test_query_params_str_validations_q_fixedquery(client: TestClient):

    private final Map<String, String> params;

    public UpgradePropertiesRuleSetup(Map<String, String> params) {
        this.params = params;
    }

    @Override
    public void execute(ViolationCheckContext context) {
        List<UpgradedProperty> currentUpgradedProperties = UpgradedProperties.parse(params.get(CURRENT_UPGRADED_PROPERTIES_KEY));

            if parameters:
                all_parameters = {
                    (param["in"], param["name"]): param for param in parameters
                }
                required_parameters = {
                    (param["in"], param["name"]): param
                    for param in parameters
                    if param.get("required")
                }