# 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 =

...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">

  `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>

        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);
        }

    input.addListener(output, rejectionPropagatingExecutor(executor, output));
    return output;
  }

  /*
   * In certain circumstances, this field might theoretically not be visible to an afterDone() call
   * triggered by cancel(). For details, see the comments on the fields of TimeoutFuture.
   */
  @CheckForNull @LazyInit ListenableFuture<? extends I> inputFuture;
  @CheckForNull @LazyInit F function;

    // --------------------------/
    // - Class/Member Variables -/
    // --------------------------/

    /**
     * Field lifecycles.
     */
    private java.util.List<Lifecycle> lifecycles;

    /**
     * Field modelEncoding.
     */
    private String modelEncoding = "UTF-8";

    // -----------/
    // - Methods -/
    // -----------/

    /**