You can also use `dataclasses` in the `response_model` parameter:

{* ../../docs_src/dataclasses/tutorial002.py hl[1,7:13,19] *}

The dataclass will be automatically converted to a Pydantic dataclass.

This way, its schema will show up in the API docs user interface:

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

## Dataclasses in Nested Data Structures { #dataclasses-in-nested-data-structures }

 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,

 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,

There's a whole chapter here in the documentation about it, you can read it at [Additional Responses in OpenAPI](additional-responses.md){.internal-link target=_blank}.

## OpenAPI Extra { #openapi-extra }

When you declare a *path operation* in your application, **FastAPI** automatically generates the relevant metadata about that *path operation* to be included in the OpenAPI schema.

/// note | Technical details

/// info

The parameter `response_class` will also be used to define the "media type" of the response.

In this case, the HTTP header `Content-Type` will be set to `application/json`.

And it will be documented as such in OpenAPI.

///

/// tip

The `ORJSONResponse` is only available in FastAPI, not in Starlette.

///

## HTML Response { #html-response }

//
// ``delete``: This is the delete-marker
//
// ``legacyObject``: This is the legacy object in xlV1 format, preserved until its overwritten
//
// The most recently updated element in the array is considered the latest version.

// In addition to these we have a special kind called free-version. This is represented
// using a delete-marker and MetaSys entries. It's used to track tiered content of a

	[op(0x00)]
	int LsarClose([in,out] policy_handle *handle);

	[op(0x07)]
	int LsarQueryInformationPolicy([in] policy_handle *handle,
			[in] uint16_t level,
			[out,switch_is(level),unique] LsarPolicyInfo *info);

	[op(0x0f)]
	int LsarLookupSids([in] policy_handle *handle,
			[in] LsarSidArray *sids,
			[out,unique] LsarRefDomainList *domains,
			[in,out] LsarTransNameArray *names,

	[op(0x00)]
	int LsarClose([in,out] policy_handle *handle);

	[op(0x07)]
	int LsarQueryInformationPolicy([in] policy_handle *handle,
			[in] uint16_t level,
			[out,switch_is(level),unique] LsarPolicyInfo *info);

	[op(0x0f)]
	int LsarLookupSids([in] policy_handle *handle,
			[in] LsarSidArray *sids,
			[out,unique] LsarRefDomainList *domains,
			[in,out] LsarTransNameArray *names,

      assertEqualsSame(expected, in, is('-').or(is('#')).collapseFrom(in, replacement));
      assertEqualsSame(expected, in, isNot('x').collapseFrom(in, replacement));
      assertEqualsSame(expected, in, is('x').negate().collapseFrom(in, replacement));
      assertEqualsSame(expected, in, anyOf("-").collapseFrom(in, replacement));
      assertEqualsSame(expected, in, anyOf("-#").collapseFrom(in, replacement));

 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,