Because the database connection is potentially I/O blocking, this dependency is created with a normal `def` function.

And then, in each *path operation function* that needs to access the database we add it as a dependency.

        dependency_scopes = depends.scopes
        security_scopes.extend(dependency_scopes)
    if isinstance(dependency, SecurityBase):
        use_scopes: List[str] = []
        if isinstance(dependency, (OAuth2, OpenIdConnect)):
            use_scopes = security_scopes
        security_requirement = SecurityRequirement(
            security_scheme=dependency, scopes=use_scopes
        )
    sub_dependant = get_dependant(

For example, `dependency_c` can have a dependency on `dependency_b`, and `dependency_b` on `dependency_a`:

=== "Python 3.9+"

    ```Python hl_lines="6  14  22"
    {!> ../../../docs_src/dependencies/tutorial008_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="5  13  21"
    {!> ../../../docs_src/dependencies/tutorial008_an.py!}
    ```

    ```Python hl_lines="26-27  30"
    {!> ../../../docs_src/dependency_testing/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="28-29  32"
    {!> ../../../docs_src/dependency_testing/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="29-30  33"
    {!> ../../../docs_src/dependency_testing/tutorial001_an.py!}
    ```

=== "Python 3.10+ nicht annotiert"

**FastAPI** は、`yield`を持つ各依存関係の「終了コード」が正しい順番で実行されていることを確認します。

例えば、`dependency_c`は`dependency_b`と`dependency_b`に依存する`dependency_a`に、依存することができます:

```Python hl_lines="4 12 20"
{!../../../docs_src/dependencies/tutorial008.py!}
```

そして、それらはすべて`yield`を使用することができます。

この場合、`dependency_c`は終了コードを実行するために、`dependency_b`（ここでは`dep_b`という名前）の値がまだ利用可能である必要があります。

そして、`dependency_b`は`dependency_a`（ここでは`dep_a`という名前）の値を終了コードで利用できるようにする必要があります。

from typing_extensions import Annotated


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b: Annotated[DepB, Depends(dependency_b)]):

    the key value sent in the query parameter automatically and provides it as the
    dependency result. But it doesn't define how to send that API key to the client.

    ## Usage

    Create an instance object and use that object as the dependency in `Depends()`.

    The dependency result will be a string containing the key value.

    ## Example

    ```python

from docs_src.dependency_testing.tutorial001 import (
    app,
    client,
    test_override_in_items,
    test_override_in_items_with_params,
    test_override_in_items_with_q,
)


def test_override_in_items_run():
    test_override_in_items()


def test_override_in_items_with_q_run():
    test_override_in_items_with_q()


def test_override_in_items_with_params_run():
    test_override_in_items_with_params()

    * The cache can be disabled per dependency declaration, using `use_cache=False` as in `Depends(your_dependency, use_cache=False)`.
    * Updated docs at: [Using the same dependency multiple times](https://fastapi.tiangolo.com/tutorial/dependencies/sub-dependencies/#using-the-same-dependency-multiple-times).
    * PR [#292](https://github.com/tiangolo/fastapi/pull/292).

**FastAPI** stellt sicher, dass der „Exit-Code“ in jeder Abhängigkeit mit `yield` in der richtigen Reihenfolge ausgeführt wird.

Beispielsweise kann `dependency_c` von `dependency_b` und `dependency_b` von `dependency_a` abhängen:

=== "Python 3.9+"

    ```Python hl_lines="6  14  22"
    {!> ../../../docs_src/dependencies/tutorial008_an_py39.py!}
    ```

=== "Python 3.8+"