Or it might be the case that you just prefer to take other courses because they adapt better to your learning style.

### Is concurrency better than parallelism?

Nope! That's not the moral of the story.

Concurrency is different than parallelism. And it is better on **specific** scenarios that involve a lot of waiting. Because of that, it generally is a lot better than parallelism for web application development. But not for everything.

```json
{"message": "Hello World"}
```

...this response will return:

```json
{
  "message": "Hello World"
}
```

Of course, you will probably find much better ways to take advantage of this than formatting JSON. 😉

## Default response class

When creating a **FastAPI** class instance or an `APIRouter` you can specify which response class to use by default.

porter.png...

    @sub_router.on_event("shutdown")
    def sub_router_shutdown() -> None:
        state.sub_router_shutdown = True

    router.include_router(sub_router)
    app.include_router(router)

    assert state.app_startup is False
    assert state.router_startup is False
    assert state.sub_router_startup is False
    assert state.app_shutdown is False
    assert state.router_shutdown is False
    assert state.sub_router_shutdown is False

import pytest
from fastapi import APIRouter, FastAPI
from fastapi.exceptions import FastAPIError
from fastapi.testclient import TestClient

app = FastAPI()

router = APIRouter()


@router.get("")
def get_empty():
    return ["OK"]


app.include_router(router, prefix="/prefix")


client = TestClient(app)


def test_use_empty():
    with client:
        response = client.get("/prefix")

...and adapt it with your database data and credentials (equivalently for MySQL, MariaDB or any other).

!!! tip

    This is the main line that you would have to modify if you wanted to use a different database.

### Create the SQLAlchemy `engine`

The first step is to create a SQLAlchemy "engine".

We will later use this `engine` in other places.

```Python hl_lines="8-10"

    class Config:
        orm_mode = True
        getter_dict = PeeweeGetterDict


class UserBase(BaseModel):
    email: str


class UserCreate(UserBase):
    password: str


class User(UserBase):
    id: int
    is_active: bool
    items: List[Item] = []

    class Config:
        orm_mode = True

                * **FastAPI** adds a reference here to the global JSON Schemas in another place in your OpenAPI instead of including it directly. This way, other applications and clients can use those JSON Schemas directly, provide better code generation tools, etc.

The generated responses in the OpenAPI for this *path operation* will be:

```JSON hl_lines="3-12"
{
    "responses": {
        "404": {

</div>

With this feature from **Pydantic v2**, your API documentation is more **precise**, and if you have autogenerated clients and SDKs, they will be more precise too, with a better **developer experience** and consistency. 🎉

## Do not Separate Schemas

Now, there are some cases where you might want to have the **same schema for input and output**.