{!> ../../../docs_src/query_params/tutorial002_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params/tutorial002.py!}
    ```

In this case, the function parameter `q` will be optional, and will be `None` by default.

!!! check

Cela signifie aussi que, dans la plupart des cas, vous pouvez fournir l'objet reçu d'une requête **directement à la base de données**, comme tout est validé automatiquement.

Inversement, dans la plupart des cas vous pourrez juste envoyer l'objet récupéré de la base de données **directement au client**

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="10"
    {!> ../../../docs_src/dependencies/tutorial011.py!}
    ```

In this case, this `__call__` is what **FastAPI** will use to check for additional parameters and sub-dependencies, and this is what will be called to pass a value to the parameter in your *path operation function* later.

## Parameterize the instance

### Understand the question

* Check if you can understand what is the **purpose** and use case of the person asking.

* Then check if the question (the vast majority are questions) is **clear**.

* In many cases the question asked is about an imaginary solution from the user, but there might be a **better** one. If you can understand the problem and use case better, you might be able to suggest a better **alternative solution**.

from fastapi import Depends, FastAPI, HTTPException, Request, Response
from sqlalchemy.orm import Session

from . import crud, models, schemas
from .database import SessionLocal, engine

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:

This way, you don't have to know beforehand what the valid field/attribute names are (as would be the case with Pydantic models).

This would be useful if you want to receive keys that you don't already know.

---

Another useful case is when you want to have keys of another type (e.g., `int`).

That's what we are going to see here.

In this case, you would accept any `dict` as long as it has `int` keys with `float` values:

```Python hl_lines="1  7-8"
{!../../../docs_src/response_headers/tutorial002.py!}
```

Posteriormente, puedes devolver cualquier objeto que necesites, como normalmente harías (un `dict`, un modelo de base de datos, etc).

Si declaraste un `response_model`, este se continuará usando para filtrar y convertir el objeto que devolviste.

# JSON互換エンコーダ

データ型（Pydanticモデルのような）をJSONと互換性のあるもの（`dict`や`list`など）に変更する必要がある場合があります。

例えば、データベースに保存する必要がある場合です。

そのために、**FastAPI** は`jsonable_encoder()`関数を提供しています。

## `jsonable_encoder`の使用

JSON互換のデータのみを受信するデータベース`fase_db`があるとしましょう。

例えば、`datetime`オブジェクトはJSONと互換性がないので、このデーターベースには受け取られません。

そのため、`datetime`オブジェクトは<a href="https://en.wikipedia.org/wiki/ISO_8601" class="external-link" target="_blank">ISO形式</a>のデータを含む`str`に変換されなければなりません。

In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks

    * `200` is the default status code, which means everything was "OK".
    * Another example would be `201`, "Created". It is commonly used after creating a new record in the database.
    * A special case is `204`, "No Content".  This response is used when there is no content to return to the client, and so the response must not have a body.