# 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`

First, you have to import it:

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


/// warning

    # fields but it's the same one, so count them by name
    body_param_names_set = {field.name for field in fields}
    # A top level field has to be a single field, not multiple
    if len(body_param_names_set) > 1:
        return True
    first_field = fields[0]
    # If it explicitly specifies it is embedded, it has to be embedded

                "Configure " + dispatcherMeta.displayName());
        context.addInHeader("");

        for (DispatcherMeta.Field field : dispatcherMeta.fields()) {
            String fieldKey = field.getKey();
            String fieldDescription = "Configure " + fieldKey + ": " + field.getDescription();
            if (field.getOptions().isPresent()) {
                // list options
                ListPromptBuilder listPromptBuilder =

func (z *xlMetaDataDirDecoder) DecodeMsg(dc *msgp.Reader) (err error) {
	var field []byte
	_ = field
	var zb0001 uint32
	zb0001, err = dc.ReadMapHeader()
	if err != nil {
		err = msgp.WrapError(err)
		return
	}
	var zb0001Mask uint8 /* 1 bits */
	_ = zb0001Mask
	for zb0001 > 0 {
		zb0001--
		field, err = dc.ReadMapKeyPtr()
		if err != nil {
			err = msgp.WrapError(err)
			return
		}

func (z *ChecksumInfo) DecodeMsg(dc *msgp.Reader) (err error) {
	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 "PartNumber":
			z.PartNumber, err = dc.ReadInt()

...then because `description` has a default value, if you **don't return anything** for that field, it will still have that **default value**.

### Model for Output Response Data

If you interact with the docs and check the response, even though the code didn't add anything in one of the `description` fields, the JSON response contains the default value (`null`):

<div class="screenshot">

func (z *allTierStats) DecodeMsg(dc *msgp.Reader) (err error) {
	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 "ts":
			var zb0002 uint32

func (z *BaseOptions) DecodeMsg(dc *msgp.Reader) (err error) {
	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) {
		default:
			err = dc.Skip()
			if err != nil {

  `hostAliases` fields to mark the fields used as keys in those lists as either defaulted
  or required. ([#124553](https://github.com/kubernetes/kubernetes/pull/124553), [@pmalek](https://github.com/pmalek))

          <field-name>source</field-name>
        </requirement>
        <requirement>
          <role>org.codehaus.plexus.PlexusContainer</role>
          <role-hint>default</role-hint>
          <field-name>container</field-name>
        </requirement>
        <requirement>
          <role>org.apache.maven.plugin.LegacySupport</role>
          <role-hint>default</role-hint>
          <field-name>legacySupport</field-name>