わかりにくくなることを防ぐためにRealmモデルとViewの部分を一緒にしてます。

まずはRealmのインストールをしてください。

ターミナルで下記を打ち込めばOKです。

flutter pub add realm

その後に下記をコピペで（クラス名は同じにするか、必要に応じて変えてください）

クラスは二つだけなので、長いように感じるかもですが、多分他のどこよりも簡単にデータ作れると思うので、お付き合いください。

main.dart

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:realm/realm.dart';

part 'main.g.dart';

@RealmModel()
class _Car {
  late String make;
  String? model;
  int? kilometers = 500;
  _Person? owner;
}

@RealmModel()
class _Person {
  late String name;
  int age = 1;
}

void main() {
  print("Current PID $pid");
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  late Realm realm;

  _MyAppState() {
    final config = Configuration([Car.schema, Person.schema]);
    realm = Realm(config);
  }

  int get carsCount => realm.all<Car>().length;

  @override
  void initState() {
    var myCar = Car("Tesla", model: "Model Y", kilometers: 1);
    realm.write(() {
    //   print('Adding a Car to Realm.');
      var car = realm.add(Car("Tesla", owner: Person("John")));
    //   print("Updating the car's model and kilometers");
    //   car.model = "Model 3";
    //   car.kilometers = 5000;
    //
    //   print('Adding another Car to Realm.');
    //   realm.add(myCar);
    //
    //   print("Changing the owner of the car.");
    //   myCar.owner = Person("me", age: 18);
    //   print("The car has a new owner ${car.owner!.name}");
    });

    // print("Getting all cars from the Realm.");
    // var cars = realm.all<Car>();
    // print("There are ${cars.length} cars in the Realm.");
    //
    // var indexedCar = cars[0];
    // print('The first car is ${indexedCar.make} ${indexedCar.model}');
    //
    // print("Getting all Tesla cars from the Realm.");
    // var filteredCars = realm.all<Car>().query("make == 'Tesla'");
    // print('Found ${filteredCars.length} Tesla cars');

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Plugin example app'),
        ),
        body: Center(
          child: Text('Running on: ${Platform.operatingSystem}.\n\nThere are $carsCount cars in the Realm.\n'),
        ),
      ),
    );
  }
}

main.g.dart(こちらもコピペでOK)

クラス名は必要に応じて変えてください。

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'main.dart';

// **************************************************************************
// RealmObjectGenerator
// **************************************************************************

class Car extends _Car with RealmEntity, RealmObject {
  static var _defaultsSet = false;

  Car(
    String make, {
    String? model,
    int? kilometers = 500,
    Person? owner,
  }) {
    if (!_defaultsSet) {
      _defaultsSet = RealmObject.setDefaults<Car>({
        'kilometers': 500,
      });
    }
    RealmObject.set(this, 'make', make);
    RealmObject.set(this, 'model', model);
    RealmObject.set(this, 'kilometers', kilometers);
    RealmObject.set(this, 'owner', owner);
  }

  Car._();

  @override
  String get make => RealmObject.get<String>(this, 'make') as String;
  @override
  set make(String value) => RealmObject.set(this, 'make', value);

  @override
  String? get model => RealmObject.get<String>(this, 'model') as String?;
  @override
  set model(String? value) => RealmObject.set(this, 'model', value);

  @override
  int? get kilometers => RealmObject.get<int>(this, 'kilometers') as int?;
  @override
  set kilometers(int? value) => RealmObject.set(this, 'kilometers', value);

  @override
  Person? get owner => RealmObject.get<Person>(this, 'owner') as Person?;
  @override
  set owner(covariant Person? value) => RealmObject.set(this, 'owner', value);

  @override
  Stream<RealmObjectChanges<Car>> get changes =>
      RealmObject.getChanges<Car>(this);

  static SchemaObject get schema => _schema ??= _initSchema();
  static SchemaObject? _schema;
  static SchemaObject _initSchema() {
    RealmObject.registerFactory(Car._);
    return const SchemaObject(Car, [
      SchemaProperty('make', RealmPropertyType.string),
      SchemaProperty('model', RealmPropertyType.string, optional: true),
      SchemaProperty('kilometers', RealmPropertyType.int, optional: true),
      SchemaProperty('owner', RealmPropertyType.object,
          optional: true, linkTarget: 'Person'),
    ]);
  }
}

class Person extends _Person with RealmEntity, RealmObject {
  static var _defaultsSet = false;

  Person(
    String name, {
    int age = 1,
  }) {
    if (!_defaultsSet) {
      _defaultsSet = RealmObject.setDefaults<Person>({
        'age': 1,
      });
    }
    RealmObject.set(this, 'name', name);
    RealmObject.set(this, 'age', age);
  }

  Person._();

  @override
  String get name => RealmObject.get<String>(this, 'name') as String;
  @override
  set name(String value) => RealmObject.set(this, 'name', value);

  @override
  int get age => RealmObject.get<int>(this, 'age') as int;
  @override
  set age(int value) => RealmObject.set(this, 'age', value);

  @override
  Stream<RealmObjectChanges<Person>> get changes =>
      RealmObject.getChanges<Person>(this);

  static SchemaObject get schema => _schema ??= _initSchema();
  static SchemaObject? _schema;
  static SchemaObject _initSchema() {
    RealmObject.registerFactory(Person._);
    return const SchemaObject(Person, [
      SchemaProperty('name', RealmPropertyType.string),
      SchemaProperty('age', RealmPropertyType.int),
    ]);
  }
}

あとは実行すればRealmのデータが作られてます。下記参照

コメントアウトしている部分は最低限Realmのデータが作られる部分だけあればいいかなと思いコメントしてあります。

コメントアウトを外せば、作られるRealmのデータが二つになるだけなので、気になる方はコメントアウトを外してもらえればと。

データの確認方法はこちらの記事で解説してますので、必要な方はこちらもどうぞ。