## Nested Models

Each attribute of a Pydantic model has a type.

But that type can itself be another Pydantic model.

So, you can declare deeply nested JSON "objects" with specific attribute names, types and validations.

All that, arbitrarily nested.

### Define a submodel

For example, we can define an `Image` model:

//// tab | Python 3.10+

    callback: AsyncDns.Callback,
  ) {
    try {
      resolver.query(
        network,
        hostname,
        dnsClass.type,
        DnsResolver.FLAG_EMPTY,
        executor,
        null,
        object : DnsResolver.Callback<List<InetAddress>> {
          override fun onAnswer(
            addresses: List<InetAddress>,
            rCode: Int,
          ) {
            callback.onResponse(hostname, addresses)
          }

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
@ElementTypesAreNonnullByDefault
public abstract class AbstractCollectionTester<E extends @Nullable Object>
    extends AbstractContainerTester<Collection<E>, E> {

  // TODO: replace this with an accessor.
  protected Collection<E> collection;

  @Override
  protected Collection<E> actualContents() {

        "components": {
            "schemas": {
                "ValidationError": {
                    "title": "ValidationError",
                    "required": ["loc", "msg", "type"],
                    "type": "object",
                    "properties": {
                        "loc": {
                            "title": "Location",
                            "type": "array",
                            "items": {

        "components": {
            "schemas": {
                "ValidationError": {
                    "title": "ValidationError",
                    "required": ["loc", "msg", "type"],
                    "type": "object",
                    "properties": {
                        "loc": {
                            "title": "Location",
                            "type": "array",
                            "items": {

// Copyright (c) 2015-2023 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful

 * the License.
 */

package com.google.common.hash;

import com.google.common.base.Supplier;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Source of {@link LongAddable} objects that deals with GWT, Unsafe, and all that.
 *
 * @author Louis Wasserman
 */
@ElementTypesAreNonnullByDefault
final class LongAddables {
  private static final Supplier<LongAddable> SUPPLIER;

  static {

  static class Subscriber {
    final List<Object> nonSubscriberEvents = Lists.newArrayList();
    final List<Object> subscriberEvents = Lists.newArrayList();

    public void notASubscriber(Object o) {
      nonSubscriberEvents.add(o);
    }

    @Subscribe
    public void subscriber(Object o) {
      subscriberEvents.add(o);
    }
  }

  public void testNonSubscriber() {

  static class Subscriber {
    final List<Object> nonSubscriberEvents = Lists.newArrayList();
    final List<Object> subscriberEvents = Lists.newArrayList();

    public void notASubscriber(Object o) {
      nonSubscriberEvents.add(o);
    }

    @Subscribe
    public void subscriber(Object o) {
      subscriberEvents.add(o);
    }
  }

  public void testNonSubscriber() {

                "Items": {
                    "title": "Items",
                    "required": ["items"],
                    "type": "object",
                    "properties": {
                        "items": {
                            "title": "Items",
                            "type": "object",
                            "additionalProperties": {"type": "integer"},
                        }
                    },