# 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

...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">

        builder.startObject();
        if (sessionId != null) {
            builder.field(SESSION_ID, sessionId);
        }
        if (ruleId != null) {
            builder.field(RULE_ID, ruleId);
        }
        if (url != null) {
            builder.field(URL, url);
        }
        if (parentUrl != null) {
            builder.field(PARENT_URL, parentUrl);
        }
        if (status != null) {

            builder.field(SESSION_ID, sessionId);
        }
        if (method != null) {
            builder.field(METHOD, method);
        }
        if (url != null) {
            builder.field(URL, url);
        }
        if (parentUrl != null) {
            builder.field(PARENT_URL, parentUrl);
        }
        if (depth != null) {
            builder.field(DEPTH, depth);
        }

        builder.startObject();
        if (sessionId != null) {
            builder.field(SESSION_ID, sessionId);
        }
        if (filterType != null) {
            builder.field(FILTER_TYPE, filterType);
        }
        if (url != null) {
            builder.field(URL, url);
        }
        builder.endObject();
        return builder;
    }

					href="#searchOptions" class="badge badge-primary"
					data-toggle="control-options"> <c:if
							test="${empty fields.label}">
							<la:message key="labels.searchoptions_all" />
						</c:if> <c:if test="${!empty fields.label}">
							<c:forEach var="sLabel" items="${fields.label}">
								<c:forEach var="item" items="${labelTypeItems}">
									<c:if test="${item.value==sLabel}">${f:h(item.label)}</c:if>

					href="#searchOptions" class="badge badge-primary"
					data-toggle="control-options"> <c:if
							test="${empty fields.label}">
							<la:message key="labels.searchoptions_all" />
						</c:if> <c:if test="${!empty fields.label}">
							<c:forEach var="sLabel" items="${fields.label}">
								<c:forEach var="item" items="${labelTypeItems}">
									<c:if test="${item.value==sLabel}">${f:h(item.label)}</c:if>

        builder.startObject();
        if (transformerName != null) {
            builder.field(TRANSFORMER_NAME, transformerName);
        }
        if (data != null) {
            builder.field(DATA, data);
        }
        if (encoding != null) {
            builder.field(ENCODING, encoding);
        }
        builder.endObject();
        return builder;
    }

                type: string
              pluginConfig:
                description: The configuration that will be passed on to the plugin.
                type: object
                x-kubernetes-preserve-unknown-fields: true
              pluginName:
                description: The plugin name to be used in the Envoy configuration
                  (used to be called `rootID`).
                maxLength: 256