They are generally all related to the same application.

The analogy in the relational database world would be a "database" (a specific database, not the database server).

The analogy in **MongoDB** would be a "collection".

In the code, a `Bucket` represents the main entrypoint of communication with the database.

This utility function will:

* Connect to a **Couchbase** cluster (that might be a single machine).

    ```
    from app.routers import items
    ```

* The `app` directory contains everything. And it has an empty file `app/__init__.py`, so it is a "Python package" (a collection of "Python modules"): `app`.
* It contains an `app/main.py` file. As it is inside a Python package (a directory with a file `__init__.py`), it is a "module" of that package: `app.main`.

After this, the client and the server have an **encrypted TCP connection**, this is what TLS provides. And then they can use that connection to start the actual **HTTP communication**.

And that's what **HTTPS** is, it's just plain **HTTP** inside a **secure TLS connection** instead of a pure (unencrypted) TCP connection.

!!! tip

FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

And it will work and will be useful **during development**.

But if your connection to the server is lost, the **running process** will probably die.

Additionally, a background task is normally an independent set of logic that should be handled separately, with its own resources (e.g. its own database connection).

```

## `Bucket` を取得する関数の追加

**Couchbase**では、bucketはdocumentのセットで、様々な種類のものがあります。

Bucketは通常、同一のアプリケーション内で互いに関係を持っています。

リレーショナルデータベースの世界でいう"database"(データベースサーバではなく特定のdatabase)と類似しています。

**MongoDB** で例えると"collection"と似た概念です。

次のコードでは主に `Bucket` を利用してCouchbaseを操作します。

この関数では以下の処理を行います:

* **Couchbase** クラスタ(1台の場合もあるでしょう)に接続
    * タイムアウトのデフォルト値を設定
* クラスタで認証を取得
* `Bucket` インスタンスを取得
    * タイムアウトのデフォルト値を設定

<img src="/img/tutorial/websockets/image03.png">

You can send (and receive) many messages:

<img src="/img/tutorial/websockets/image04.png">

And all of them will use the same WebSocket connection.

## Using `Depends` and others

In WebSocket endpoints you can import from `fastapi` and use:

* `Depends`
* `Security`
* `Cookie`
* `Header`
* `Path`
* `Query`

```Python hl_lines="18-20"
{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

For the **next request**, as we will reset that context variable again in the `async` dependency `reset_db_state()` and then create a new connection in the `get_db()` dependency, that new request will have its own database state (connection, transactions, etc).

!!! tip

# Test Client - `TestClient`

You can use the `TestClient` class to test FastAPI applications without creating an actual HTTP and socket connection, just communicating directly with the FastAPI code.

Read more about it in the [FastAPI docs for Testing](https://fastapi.tiangolo.com/tutorial/testing/).

You can import it directly from `fastapi.testclient`:

```python
from fastapi.testclient import TestClient
```