```Python
item: Item
```

...and with that single declaration you get:

* Editor support, including:
    * Completion.
    * Type checks.
* Validation of data:
    * Automatic and clear errors when the data is invalid.
    * Validation even for deeply nested JSON objects.

            if ( log.isDebugEnabled() ) {
                log.debug(
                    String.format(
                        "PAC signature validation failed, have: %s expected: %s type: %d len: %d",
                        Hexdump.toHexString(checksum),
                        Hexdump.toHexString(this.serverSignature.getChecksum()),

     *
     * @return The severity level of this problem, never {@code null}.
     */
    Severity getSeverity();

    /**
     * Gets the applicable maven version/validation level of this problem
     * @return The version, never {@code null}.
     */
    Version getVersion();

使用上面的任何方法，它在 `/docs` 中看起来都是这样的:

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

## 技术细节

关于 `example` 和 `examples`...

JSON Schema在最新的一个版本中定义了一个字段 <a href="https://json-schema.org/draft/2019-09/json-schema-validation.html#rfc.section.9.5" class="external-link" target="_blank">`examples`</a> ，但是 OpenAPI 基于之前的一个旧版JSON Schema，并没有 `examples`.

                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

                    "schema": {
                        "$ref": "#/components/schemas/Item"
                    }
                }
            }
        },
        "422": {
            "description": "Validation Error",
            "content": {
                "application/json": {
                    "schema": {
                        "$ref": "#/components/schemas/HTTPValidationError"
                    }
                }

                                }
                            },
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

	}

	if policies[0] != "consoleAdmin" {
		t.Fatalf("expected 'consoleAdmin', %s", policies[0])
	}
}

// TestSkipContentSha256Cksum - Test validate the logic which decides whether
// to skip checksum validation based on the request header.
func TestSkipContentSha256Cksum(t *testing.T) {
	testCases := []struct {
		inputHeaderKey   string
		inputHeaderValue string

		inputQueryKey   string
		inputQueryValue string

import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;
import org.lastaflute.web.ruts.process.ActionRuntime;
import org.lastaflute.web.validation.VaErrorHook;
import org.lastaflute.web.validation.exception.ValidationErrorException;

import jakarta.annotation.Resource;

/**
 * @author shinsuke
 * @author Keiichi Watanabe
 */

So, even with the code above that doesn't use Pydantic explicitly, FastAPI is using Pydantic to convert those standard dataclasses to Pydantic's own flavor of dataclasses.

And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

/// info