Stellen Sie sich vor, Sie entwickeln eine Anwendung, mit der Sie Rechnungen erstellen können.

Diese Rechnungen haben eine `id`, einen optionalen `title`, einen `customer` (Kunde) und ein `total` (Gesamtsumme).

Der Benutzer Ihrer API (ein externer Entwickler) erstellt mit einem POST-Request eine Rechnung in Ihrer API.

Dann wird Ihre API (beispielsweise):

👉 💼, 👆 💪 💚 📄 ❔ 👈 🔢 🛠️ *🔜* 👀 💖. ⚫️❔ *➡ 🛠️* ⚫️ 🔜 ✔️, ⚫️❔ 💪 ⚫️ 🔜 ⌛, ⚫️❔ 📨 ⚫️ 🔜 📨, ♒️.

## 📱 ⏮️ ⏲

➡️ 👀 🌐 👉 ⏮️ 🖼.

🌈 👆 🛠️ 📱 👈 ✔ 🏗 🧾.

👉 🧾 🔜 ✔️ `id`, `title` (📦), `customer`, & `total`.

👩‍💻 👆 🛠️ (🔢 👩‍💻) 🔜 ✍ 🧾 👆 🛠️ ⏮️ 🏤 📨.

⤴️ 👆 🛠️ 🔜 (➡️ 🌈):

* 📨 🧾 🕴 🔢 👩‍💻.
* 📈 💸.
* 📨 📨 🔙 🛠️ 👩‍💻 (🔢 👩‍💻).

    ```

Das würde bedeuten, dass **FastAPI** einen Body erwartet wie:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

Wiederum, nur mit dieser Deklaration erhalten Sie von **FastAPI**:

from fastapi import APIRouter, FastAPI
from pydantic import BaseModel, HttpUrl

app = FastAPI()


class Invoice(BaseModel):
    id: str
    title: Union[str, None] = None
    customer: str
    total: float


class InvoiceEvent(BaseModel):
    description: str
    paid: bool


class InvoiceEventReceived(BaseModel):
    ok: bool


invoices_callback_router = APIRouter()

Это означает, что **FastAPI** будет ожидать тело запроса, аналогичное этому:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

Ещё раз: сделав такое объявление, с помощью **FastAPI** вы получите:

For example, if your code loads a Machine Learning model with **1 GB in size**, when you run one process with your API, it will consume at least 1 GB of RAM. And if you start **4 processes** (4 workers), each will consume 1 GB of RAM. So in total, your API will consume **4 GB of RAM**.

And if your remote server or virtual machine only has 3 GB of RAM, trying to load more than 4 GB of RAM will cause problems. 🚨

### Multiple Processes - An Example

### Est-ce que la concurrence est mieux que le parallélisme ?

Nope ! C'est ça la morale de l'histoire.

### Concorrência é melhor que paralelismo?

Não! Essa não é a moral da história.

    @app.get("/model/{name}", response_model=ModelA)
    async def get_model_a(name: str, model_c=Depends(get_model_c)):
        return {"name": name, "description": "model-a-desc", "foo": model_c}

    client = TestClient(app)
    return client


@needs_pydanticv2
def test_filter_sub_model(client: TestClient):
    response = client.get("/model/modelA")
    assert response.status_code == 200, response.text

```

이는 **FastAPI**가 다음과 유사한 본문을 기대한다는 것을 의미합니다:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

다시 한번, **FastAPI**를 사용하여 해당 선언을 함으로써 얻는 것은:

* 중첩 모델도 편집기 지원(자동완성 등)
* 데이터 변환