Mesmo que o sistema hierárquico de injeção de dependência seja simples de definir e utilizar, ele ainda é bastante poderoso.

Você pode definir dependências que por sua vez definem suas próprias dependências.

No fim, uma árvore hierárquica de dependências é criadas, e o sistema de **Injeção de Dependência** toma conta de resolver todas essas dependências (e as sub-dependências delas) para você, e provê (injeta) os resultados em cada passo.

Also fügen wir sie in ihr eigenes `dependencies`-Modul (`app/dependencies.py`) ein.

Wir werden nun eine einfache Abhängigkeit verwenden, um einen benutzerdefinierten `X-Token`-Header zu lesen:

{* ../../docs_src/bigger_applications/app_an_py39/dependencies.py hl[3,6:8] title["app/dependencies.py"] *}

/// tip | Tipp

Параметры `prefix`, `tags`, `responses` и `dependencies` относятся к функционалу **FastAPI**, помогающему избежать дублирования кода.

///

### Импорт зависимостей { #import-the-dependencies }

Наш код находится в модуле `app.routers.items` (файл `app/routers/items.py`).

И нам нужно вызвать функцию зависимости из модуля `app.dependencies` (файл `app/dependencies.py`).

     * Sets the project to resolve dependencies for.
     *
     * @param project The project to resolve dependencies for, may be {@code null}.
     * @return This request for chaining, never {@code null}.
     */
    DependencyResolutionRequest setMavenProject(MavenProject project);

    /**
     * Gets the filter used to exclude some dependencies from resolution.
     *

You can define dependencies that in turn can define dependencies themselves.

In the end, a hierarchical tree of dependencies is built, and the **Dependency Injection** system takes care of solving all these dependencies for you (and their sub-dependencies) and providing (injecting) the results at each step.

}

/**
 * Walk the resolved graph and discover all external dependencies that are not transitive dependencies
 * of project dependencies. This optimizes module loading during runtime, as we will only load external
 * modules that are not loaded transitively by other project modules.
 *
 * We perform this filtering, since if we simply include all external dependencies, regardless of whether

## `Security` em decoradores de `dependencies` { #security-in-decorator-dependencies }

* 所有的这些*路径操作*都将在自身之前计算/执行 `dependencies` 列表。
    * 如果你还在一个具体的*路径操作*中声明了依赖项，**它们也会被执行**。
    * 路由器的依赖项最先执行，然后是[装饰器中的 `dependencies`](dependencies/dependencies-in-path-operation-decorators.md){.internal-link target=_blank}，再然后是普通的参数依赖项。
    * 你还可以添加[具有 `scopes` 的 `Security` 依赖项](../advanced/security/oauth2-scopes.md){.internal-link target=_blank}。

/// tip

在 `APIRouter`中具有 `dependencies` 可以用来，例如，对一整组的*路径操作*要求身份认证。即使这些依赖项并没有分别添加到每个路径操作中。

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.apache.maven.its</groupId>
                <artifactId>bom</artifactId>
                <version>0.1</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>

    }
}
notForAccessorGeneration {
    dependencies {
        sharedArchTestClasses(project(":internal-architecture-testing"))
    }
}

testing {
    suites {
        create("archTest", JvmTestSuite::class) {
            project.jvmCompile {
                addCompilationFrom(sources)
            }

            dependencies {
                implementation(project.dependencies.create(project))