# Dependencies - `Depends()` and `Security()`

## `Depends()`

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

    {!> ../../../docs_src/dependencies/tutorial012_an.py!}
    ```

=== "Python 3.8 nicht annotiert"

    !!! tip "Tipp"
        Bevorzugen Sie die `Annotated`-Version, falls möglich.

    ```Python hl_lines="15"
    {!> ../../../docs_src/dependencies/tutorial012.py!}
    ```

    ```

=== "Python 3.8 Annotated가 없는 경우"

    !!! tip "팁"
        가능하다면 `Annotated`가 달린 버전을 권장합니다.

    ```Python hl_lines="15"
    {!> ../../../docs_src/dependencies/tutorial012.py!}
    ```

그리고 [*경로 작동 데코레이터*에 `dependencies` 추가하기](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}에 대한 아이디어는 여전히 적용되지만 여기에서는 앱에 있는 모든 *경로 작동*에 적용됩니다.

## *경로 작동* 모음에 대한 의존성

Nils Lindemann <******@****.***> 1711822605 +0100

Dazu deklarieren wir eine Methode `__call__`:

=== "Python 3.9+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/dependencies/tutorial011_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/dependencies/tutorial011_an.py!}
    ```

=== "Python 3.8+ nicht annotiert"

    !!! tip "Tipp"
        Bevorzugen Sie die `Annotated`-Version, falls möglich.

# Sub-dependencies

You can create dependencies that have **sub-dependencies**.

They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable"

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

=== "Python 3.10+"

    ```Python hl_lines="8-9"
    {!> ../../../docs_src/dependencies/tutorial005_an_py310.py!}
    ```

=== "Python 3.9+"

# Advanced Dependencies

## Parameterized dependencies

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

```Python hl_lines="8 9"
{!../../../docs_src/dependencies/tutorial005.py!}
```

これはオプショナルのクエリパラメータ`q`を`str`として宣言し、それを返すだけです。

これは非常にシンプルです（あまり便利ではありません）が、サブ依存関係がどのように機能するかに焦点を当てるのに役立ちます。

### 第二の依存関係 「依存可能なもの」と「依存」

そして、別の依存関数（「依存可能なもの」）を作成して、同時にそれ自身の依存関係を宣言することができます（つまりそれ自身も「依存」です）:

```Python hl_lines="13"
{!../../../docs_src/dependencies/tutorial005.py!}
```

宣言されたパラメータに注目してみましょう:

# Testing Dependencies with Overrides

## Overriding dependencies during testing

There are some scenarios where you might want to override a dependency during testing.

You don't want the original dependency to run (nor any of the sub-dependencies it might have).

# Global Dependencies

For some types of applications you might want to add dependencies to the whole application.

Similar to the way you can [add `dependencies` to the *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, you can add them to the `FastAPI` application.

In that case, they will be applied to all the *path operations* in the application:

=== "Python 3.9+"

    ```Python hl_lines="16"