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

​

//https://stackoverflow.com/questions/52797153/how-to-determine-if-a-json-object-contains-only-a-specific-key

​

    class TestClass

    {

        public static void Test()

        {

            int count = 0;

​

            var jObject = JObject.Parse(GetJson());

            foreach (var category in jObject["Categories"].OfType<JObject>())

            {

                var result = category.Count == 1 && category.Property("Name") != null;

                Console.WriteLine("Result for Category \"{0}\" = {1}:", category["Name"], result);

                Console.WriteLine("   " + category.ToString(Formatting.None));

                if (result)

                    count++;

            }

            Assert.IsTrue(count == 4, string.Format("Wrong number of objects {0} selected!", count));

        }   

        static string GetJson()

        {

            var json = @"{

    ""Name"": ""ThirdParty"",

    ""Categories"": [

        { ""Name"": ""Identity"" },

        {

            ""Name"": ""Contact Information"",

            ""Mandatory"": true,

            ""Fields"": [

                { ""Name"": ""Phones"" },

                { ""Name"": ""Faxes"" },

                { ""Name"": ""Emails"" }

            ]

        },

        { ""Name"": ""Addresses"" },

        { ""Name"": ""Bank Accounts"" },

        { },

        { ""No Name"": ""this object has no Name property and so should have been filtered out"" },

        { ""Name"": ""Test data"" },

    ]

}

";

            return json;

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​