using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Data;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

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

​

//https://stackoverflow.com/questions/77834272/create-newtonsoft-json-linq-jarray-from-another-array-with-different-structure

​

    class TestClass

    {

        public static void Test()

        {

            var jsonString = GetJson();

            // Parse (or load from a stream) the incoming JSON as a JArray

            var array = JArray.Parse(jsonString);

​

            var query = array

                .OfType<JObject>()

                .Select(o => 

                       new JObject

                       {

                           {"Fields", new JArray(o.Properties().Select(p => new JObject{{"Key", p.Name}, {"Value", p.Value}}))},

                       });

            var newArray = new JArray(query);

            Console.WriteLine(newArray);

            Assert.That(JToken.DeepEquals(JArray.Parse(GetRequiredJson()), newArray));

        }   

        static string GetJson() =>

            """

            [

              {

                "Relationship": "child",

                "FirstName": "Alex"

              }

            ]           

            """;

        static string GetRequiredJson() =>

            """

            [

              {

                "Fields": [

                  {

                    "Value": "child",

                    "Key": "Relationship"

                  },

                  {

                    "Value": "Alex",

                    "Key": "FirstName"

                  }

                ]

              }

            ]

            """;

    }

​

    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;

            }

        }

    }

​