using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

    // Auto generated by https://json2csharp.com/

    // See also https://stackoverflow.com/questions/21611674/how-to-auto-generate-a-c-sharp-class-file-from-a-json-string

​

    public class Rate

    {

        public string ExternalRateId { get; set; }

    }

​

    public class RateCard

    {

        public string ExternalRateCardId { get; set; }

        public List<Rate> Rates { get; set; }

        public bool IsUpdate { get; set; }

    }

​

    public class Root

    {

        public List<RateCard> RateCards { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var json = GetJson();

            var root = JsonConvert.DeserializeObject<Root>(json);

            var externalRateIds = root.RateCards.SelectMany(r => r.Rates).Select(r => r.ExternalRateId).ToArray();

            Console.WriteLine(JsonConvert.SerializeObject(externalRateIds));

        }   

        static string GetJson() =>@"{

  ""RateCards"": [{

    ""ExternalRateCardId"": ""62283ab4"",

    ""Rates"": [{

      ""ExternalRateId"": ""2a77db10"",

    }],

    ""IsUpdate"": false

  }, {

    ""ExternalRateCardId"": ""f6878b23"",

    ""Rates"": [{

      ""ExternalRateId"": ""2a739550"",

    }],

    ""IsUpdate"": false

  }, {

    ""ExternalRateCardId"": ""3f51162c"",

    ""Rates"": [{

      ""ExternalRateId"": ""2a751bf0"",

    }],

    ""IsUpdate"": false

  }]

}

";

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Namespace, typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​