# 请求体 - 字段

与在*路径操作函数*中使用 `Query`、`Path` 、`Body` 声明校验与元数据的方式一样，可以使用 Pydantic 的 `Field` 在 Pydantic 模型内部声明校验和元数据。

## 导入 `Field`

首先，从 Pydantic 中导入 `Field`：

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

/// warning | 警告

注意，与从 `fastapi` 导入 `Query`，`Path`、`Body` 不同，要直接从 `pydantic` 导入 `Field` 。

///

## 声明模型属性

然后，使用 `Field` 定义模型的属性：

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[11:14] *}

    void constructor_shouldInitializeFields() throws Exception {
        // Verify configuration is set
        Field configField = NameServicePacket.class.getDeclaredField("config");
        configField.setAccessible(true);
        assertSame(mockConfig, configField.get(response));

        // Verify queryAddress is set
        Field queryAddressField = NodeStatusResponse.class.getDeclaredField("queryAddress");

Puedes leer más al respecto en la documentación de [Dependencias con `yield` - Salida temprana y `scope`](../tutorial/dependencies/dependencies-with-yield.md#early-exit-and-scope).

### Dependencias con `yield` y `StreamingResponse`, detalles técnicos { #dependencies-with-yield-and-streamingresponse-technical-details }

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel, Field

app = FastAPI()


class Item(BaseModel):
    name: str = Field(examples=["Foo"])
    description: Union[str, None] = Field(default=None, examples=["A very nice Item"])
    price: float = Field(examples=[35.4])
    tax: Union[float, None] = Field(default=None, examples=[3.2])


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

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

First, you have to import it:

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


/// warning

Notice that `Field` is imported directly from `pydantic`, not from `fastapi` as are all the rest (`Query`, `Path`, `Body`, etc).

///

        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        final String field = getSearchField(context.getDefaultField(), wildcardQuery.getField());
        if (Constants.DEFAULT_FIELD.equals(field)) {
            final String text = wildcardQuery.getTerm().text();
            context.addFieldLog(field, text);
            final String highlightText = StringUtils.strip(text, "*");

            // Verify the fields were set correctly using reflection
            Field oplockLevelField = Smb2OplockBreakNotification.class.getDeclaredField("oplockLevel");
            oplockLevelField.setAccessible(true);
            assertEquals(expectedOplockLevel, oplockLevelField.get(notification));

            Field fileIdField = Smb2OplockBreakNotification.class.getDeclaredField("fileId");

	var field []byte
	_ = field
	var zb0001 uint32
	zb0001, err = dc.ReadMapHeader()
	if err != nil {
		err = msgp.WrapError(err)
		return
	}
	for zb0001 > 0 {
		zb0001--
		field, err = dc.ReadMapKeyPtr()
		if err != nil {
			err = msgp.WrapError(err)
			return
		}
		switch msgp.UnsafeString(field) {
		case "Name":
			z.Name, err = dc.ReadString()

						obj := db.Statement.ReflectValue.Index(i)
						if reflect.Indirect(obj).Kind() != reflect.Struct {
							break
						}
						if _, zero := rel.Field.ValueOf(db.Statement.Context, obj); !zero { // check belongs to relation value
							rv := rel.Field.ReflectValueOf(db.Statement.Context, obj) // relation reflect value
							if !isPtr {
								rv = rv.Addr()
							}
							objs = append(objs, obj)

import java.lang.reflect.Field;

/**
 * Signals that a field could not be made accessible.
 */
public class BeanFieldSetAccessibleFailureException extends ClRuntimeException {
    private static final long serialVersionUID = 1L;

    /**
     * The target class.
     */
    protected final Class<?> targetClass;

    /**
     * The target field.
     */