* FastAPI provides more features on top of Starlette. Features that you almost always need when building APIs, like data validation and serialization. And by using it, you get automatic documentation for free (the automatic documentation doesn't even add overhead to running applications, it is generated on startup).

This is because FastAPI uses this `root_path` to create the default `server` in OpenAPI with the URL provided by `root_path`.

## Additional servers

!!! warning
    This is a more advanced use case. Feel free to skip it.

By default, **FastAPI** will create a `server` in the OpenAPI schema with the URL for the `root_path`.

* `@app.post()`
* `@app.put()`
* `@app.delete()`

And the more exotic ones:

* `@app.options()`
* `@app.head()`
* `@app.patch()`
* `@app.trace()`

!!! tip
    You are free to use each operation (HTTP method) as you wish.

    **FastAPI** doesn't enforce any specific meaning.

    The information here is presented as a guideline, not a requirement.

In this case, it would be better to get **one extra server** and run some processes on it so that they all have **enough RAM and CPU time**.

您可以在[Project Generation - Template](https://fastapi.tiangolo.com/zh/project-generation/)的模板中找到一个 FastAPI 项目中的 Alembic 示例。具体在[`alembic`代码目录中](https://github.com/tiangolo/full-stack-fastapi-postgresql/tree/master/src/backend/app/alembic/)。

### 创建依赖项

现在使用我们在`sql_app/database.py`文件中创建的`SessionLocal`来创建依赖项。

我们需要每个请求有一个独立的数据库会话/连接（`SessionLocal`），在所有请求中使用相同的会话，然后在请求完成后关闭它。

然后将为下一个请求创建一个新会话。

* 🐛 Fix overriding MKDocs theme lang in hook. PR [#10490](https://github.com/tiangolo/fastapi/pull/10490) by [@tiangolo](https://github.com/tiangolo).
* 🔥 Drop/close Gitter chat. Questions should go to GitHub Discussions, free conversations to Discord.. PR [#10485](https://github.com/tiangolo/fastapi/pull/10485) by [@tiangolo](https://github.com/tiangolo).

## 0.104.0

## Features

👆 💪 🔎 🖼 ⚗ FastAPI 🏗 📄 ⚪️➡️ [🏗 ⚡ - 📄](../project-generation.md){.internal-link target=_blank}. 🎯 <a href="https://github.com/tiangolo/full-stack-fastapi-postgresql/tree/master/src/backend/app/alembic/" class="external-link" target="_blank"> `alembic` 📁 ℹ 📟</a>.

### ✍ 🔗

🔜 ⚙️ `SessionLocal` 🎓 👥 ✍ `sql_app/database.py` 📁 ✍ 🔗.

    Use the chat only for other general conversations.

### Don't use the chat for questions

Keep in mind that as chats allow more "free conversation", it's easy to ask questions that are too general and more difficult to answer, so, you might not receive answers.

!!! note
    `PATCH` is less commonly used and known than `PUT`.

    And many teams use only `PUT`, even for partial updates.

    You are **free** to use them however you want, **FastAPI** doesn't impose any restrictions.

    But this guide shows you, more or less, how they are intended to be used.

### Using Pydantic's `exclude_unset` parameter

!!! warning
    These are very technical details about the standards **JSON Schema** and **OpenAPI**.

    If the ideas above already work for you, that might be enough, and you probably don't need these details, feel free to skip them.

Before OpenAPI 3.1.0, OpenAPI used an older and modified version of **JSON Schema**.

JSON Schema didn't have `examples`, so OpenAPI added it's own `example` field to its own modified version.