{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

## Dependency override

Now we create the dependency override and add it to the overrides for our app.

```Python hl_lines="19-24  27"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

!!! tip
    The code for `override_get_db()` is almost exactly the same as for `get_db()`, but in `override_get_db()` we use the `TestingSessionLocal` for the testing database instead.

```

## 🔗 🔐

🔜 👥 ✍ 🔗 🔐 & 🚮 ⚫️ 🔐 👆 📱.

```Python hl_lines="19-24  27"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

!!! tip
    📟 `override_get_db()` 🌖 ⚫️❔ 🎏 `get_db()`, ✋️ `override_get_db()` 👥 ⚙️ `TestingSessionLocal` 🔬 💽 ↩️.

## 💯 📱

⤴️ 👥 💪 💯 📱 🛎.

```Python hl_lines="32-47"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

!!! danger
    This is an "advanced" feature.

    If you are just starting with **FastAPI** you might want to skip this section.

## Overriding the defaults

Using the information above, you can use the same utility function to generate the OpenAPI schema and override each part that you need.

For example, let's add <a href="https://github.com/Rebilly/ReDoc/blob/master/docs/redoc-vendor-extensions.md#x-logo" class="external-link" target="_blank">ReDoc's OpenAPI extension to include a custom logo</a>.

It won't do any data conversion with Pydantic models, it won't convert the contents to any type, etc.

This gives you a lot of flexibility. You can return any data type, override any data declaration or validation, etc.

## Using the `jsonable_encoder` in a `Response`

Because **FastAPI** doesn't do any change to a `Response` you return, you have to make sure it's contents are ready for it.

```

### Using the *path operation function* name as the operationId

If you want to use your APIs' function names as `operationId`s, you can iterate over all of them and override each *path operation's* `operation_id` using their `APIRoute.name`.

You should do it after adding all your *path operations*.

```Python hl_lines="2  12-21  24"

In this case, you can override the dependency that calls that provider, and use a custom dependency that returns a mock user, only for your tests.

### Use the `app.dependency_overrides` attribute

For these cases, your **FastAPI** application has an attribute `app.dependency_overrides`, it is a simple `dict`.

## Override the default exception handlers

**FastAPI** has some default exception handlers.

These handlers are in charge of returning the default JSON responses when you `raise` an `HTTPException` and when the request has invalid data.

You can override these exception handlers with your own.

### Override request validation exceptions

FastAPI includes some default configuration parameters appropriate for most of the use cases.

It includes these default configurations:

```Python
{!../../../fastapi/openapi/docs.py[ln:7-23]!}
```

You can override any of them by setting a different value in the argument `swagger_ui_parameters`.

For example, to disable `deepLinking` you could pass these settings to `swagger_ui_parameters`:

```Python hl_lines="3"