* Those schemas will be part of the generated OpenAPI schema, and used by the automatic documentation <abbr title="User Interfaces">UIs</abbr>.

## Automatic docs { #automatic-docs }

The JSON Schemas of your models will be part of your OpenAPI generated schema, and will be shown in the interactive API docs:

<img src="/img/tutorial/body/image01.png">

The contents that you return from your *path operation function* will be put inside of that `Response`.

/// note

If you use a response class with no media type, FastAPI will expect your response to have no content, so it will not document the response format in its generated OpenAPI docs.

///

## JSON Responses { #json-responses }

///

**FastAPI** will do the automatic conversion from the request, so that the parameter `item` receives its specific content and the same for `user`.

It will perform the validation of the compound data, and will document it like that for the OpenAPI schema and automatic docs.

## Singular values in body { #singular-values-in-body }

 *
 * <ul>
 *   <li>Each {@code Closeable} resource that is successfully registered will be closed later.
 *   <li>If a {@code Throwable} is thrown in the try block, no exceptions that occur when attempting
 *       to close resources will be thrown from the finally block. The throwable from the try block
 *       will be thrown.
 *   <li>If no exceptions or errors were thrown in the try block, the <i>first</i> exception thrown

        * In requests, a list will be read, eliminating duplicates and converting it to a `set`.
        * In responses, the `set` will be converted to a `list`.
        * The generated schema will specify that the `set` values are unique (using JSON Schema's `uniqueItems`).
* `bytes`:
    * Standard Python `bytes`.
    * In requests and responses will be treated as `str`.

<img src="/img/tutorial/separate-openapi-schemas/image02.png">
</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

// If the call is canceled through the context,
// the appropriate error will be returned.
type Stream struct {
	// responses from the remote server.
	// Channel will be closed after error or when remote closes.
	// All responses *must* be read by the caller until either an error is returned or the channel is closed.
	// Canceling the context will cause the context cancellation error to be returned.
	responses <-chan Response

    * This will be used by the **automatic docs**.
    * It will also be used by automatic client code generation tools.
* **Serialize** the returned data to JSON using Pydantic, which is written in **Rust**, so it will be **much faster**.

But most importantly:

* It will **limit and filter** the output data to what is defined in the return type.

are absent from the original request, including `Content-Length`, `Transfer-Encoding`, `User-Agent`, `Host`, `Connection`, and `Content-Type`. It will add an `Accept-Encoding` header for transparent response compression unless the header is already present. If you’ve got cookies, OkHttp will add a `Cookie` header with them.

Some requests will have a cached response. When this cached response isn’t fresh, OkHttp can do a _conditional GET_ to download an updated response if it’s newer than...

   * Response and normal event sequences will not be received.
   *
   * This event will only be received when a Cache is configured for the client.
   */
  open fun cacheHit(
    call: Call,
    response: Response,
  ) {
  }

  /**
   * Invoked when a response will be served from the network. The Response will be
   * available from normal event sequences.
   *