private static void GetCarHolderAndAddCar(IServiceProvider serviceProvider)
        {
            using SampleContext context = serviceProvider.GetRequiredService <SampleContext>();

            CarHolder carHolder = context.CarHolders.First();
            Car       car       = new Car("Skoda Fabia", new Specs(4, 1035, 90));

            carHolder.AddCar(car);

            Console.WriteLine($"Adding {car.Name} ({car.Specs}) to {carHolder.Name}");
            Console.WriteLine();
        }
        private static void AddCarHolders(IServiceProvider serviceProvider)
        {
            using SampleContext context = serviceProvider.GetRequiredService <SampleContext>();

            CarHolder carHolder1 = new CarHolder("Christopher");

            carHolder1.AddCar(new Car("Opel Meriva", new Specs(4, 1455, 120)));
            context.CarHolders.Add(carHolder1);

            CarHolder carHolder2 = new CarHolder("Christoph");

            carHolder2.AddCar(new Car("Tesla Model 3", new Specs(4, 1906, 440)));
            context.CarHolders.Add(carHolder2);

            context.SaveChanges();
        }