},
                                },
                            },
                            "description": "Validation Error",
                        },
                    },
                    "summary": "Read Root",
                },
            },
        },
        "components": {
            "schemas": {

    }
}
```

Again, doing just that declaration, with **FastAPI** you get:

* Editor support (completion, etc.), even for nested models
* Data conversion
* Data validation
* Automatic documentation

## Special types and validation { #special-types-and-validation }

Apart from normal singular types like `str`, `int`, `float`, etc. you can use more complex singular types that inherit from `str`.

import jcifs.smb.SmbException;

/**
 * Validator for SMB server responses to prevent buffer overflow and injection attacks.
 *
 * Features:
 * - Buffer bounds checking
 * - Integer overflow prevention
 * - Size validation
 * - Protocol compliance checking
 * - Malformed response detection
 */
public class ServerResponseValidator {

    private static final Logger log = LoggerFactory.getLogger(ServerResponseValidator.class);

import org.codelibs.fess.app.web.admin.dict.mapping.EditForm;

/**
 * Request body class for mapping dictionary edit operations in the admin REST API.
 * This class extends EditForm to inherit the necessary form validation and binding capabilities
 * for mapping dictionary management operations.
 */
public class EditBody extends EditForm {

    /**
     * Default constructor.
     */
    public EditBody() {
        super();

import org.codelibs.fess.app.web.admin.dict.synonym.EditForm;

/**
 * Request body class for synonym dictionary edit operations in the admin REST API.
 * This class extends EditForm to inherit the necessary form validation and binding capabilities
 * for synonym dictionary management operations.
 */
public class EditBody extends EditForm {

    /**
     * Default constructor.
     */
    public EditBody() {
        super();

                                    },
                                },
                            },
                            "description": "Validation Error",
                        },
                    },
                    "summary": "Read Item",
                },
            },
        },
        "components": {
            "schemas": {

import static org.codelibs.core.misc.AssertionUtil.assertArgumentNotNull;

import java.io.File;
import java.net.URL;

import javax.xml.transform.Source;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;

import org.codelibs.core.exception.SAXRuntimeException;
import org.xml.sax.SAXException;

/**
 * Utility class for {@link Schema}.
 *
 * @author koichik
 */

# Body - Fields { #body-fields }

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field` { #import-field }

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

import org.codelibs.fess.app.web.admin.scheduler.EditForm;

/**
 * Request body class for scheduler edit operations in the admin REST API.
 * This class extends EditForm to inherit the necessary form validation and binding capabilities
 * for scheduler management operations.
 */
public class EditBody extends EditForm {

    /**
     * Flag indicating whether the scheduler job is currently running.
     */

    return PlainTextResponse(str(exc.detail), status_code=exc.status_code)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc: RequestValidationError):
    message = "Validation errors:"
    for error in exc.errors():
        message += f"\nField: {error['loc']}, Error: {error['msg']}"
    return PlainTextResponse(message, status_code=400)


@app.get("/items/{item_id}")