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 System.Collections.ObjectModel;

​

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/66446158/using-linq-in-jarray

​

#if false

Your LINQ query can be implemented as follows:

​

    var id = "2";

    var city = (string)json["departments"]

        .Where(o => o[id] != null) // From the departments array, select the object where the required id property exists

        .Select(o => o[id]["city"]).SingleOrDefault(); // An extract the value of "city" from the nested object.

​

Alternatively, you could use [`SelectToken()`](https://www.newtonsoft.com/json/help/html/QueryJsonSelectTokenJsonPath.htm) for this purpose:

​

    var id = 2;

    var path = $"departments[*].{id}.city"; // departments[*].2.city

    var city = (string)json.SelectToken(path);

​

`SelectToken()` supports [JSONPath syntax](https://goessner.net/articles/JsonPath/), and `[*]` is the JSONPath wildcard indicating that all array items should be searched.

​

Demo fiddle [here](https://dotnetfiddle.net/b1usfP).

#endif

​

    class TestClass

    {

        public static void Test()

        {

            TestLINQ();

            TestLINQ2();

            TestJsonPath();

        }

        public static void TestJsonPath()

        {

            var json = JToken.Parse(GetJson());

​

            var id = "2";

            var path = $"departments[*].{id}.city"; // departments[*].2.city

            var city = (string)json.SelectToken(path);

            Console.WriteLine(city);

            Assert.AreEqual("Petersburg", city);

        }   

​

        public static void TestLINQ()

        {

            var json = JToken.Parse(GetJson());

​

            var id = "2";

            var city = (string)json["departments"]

                .Where(o => o[id] != null) // From the departments array, select the object where the required id property exists

                .Select(o => o[id]["city"]).SingleOrDefault(); // An extract the value of "city" from the nested object.

            Console.WriteLine(city);

​

            Assert.AreEqual("Petersburg", city);

        }   

        static void TestLINQ2()

        {

            var json = JToken.Parse(GetJson());

​

            var id = "2";

            var city = (string)json["departments"]

                .SelectMany(i => i) // Use SelectMany() to project the properties of the array items to a flat enumerable 

                .Cast<JProperty>()  // Cast them to JProperty

                .Where(p => p.Name == id) // Now you can use Name

                .Select(p => p.Value["city"])

                .SingleOrDefault();

​

            Console.WriteLine(city);

​

            Assert.AreEqual("Petersburg", city);

        }

        static string GetJson()

        {

            return @"{

  ""departments"": [

    {

      ""2"": {""city"": ""Petersburg"", ""employees"": ""1200""}

    },

    {

      ""1"": {""city"": ""Ekaterinburg"", ""employees"": ""4000""}

    }

  ]

}

";

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

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

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​