https://stackoverflow.com/questions/77856068/c-sharp-how-can-i-check-if-a-field-exists-before-trying-to-query-it-in-a-json

CSharp · Console

/Program.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

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/77856068/c-sharp-how-can-i-check-if-a-field-exists-before-trying-to-query-it-in-a-json
    class TestClass
    {
        public static void Test()
		{
			Test0();
			
			Console.WriteLine();
			
			Test1();
			Test2();
		}
		
        public static void Test0()
        {
			foreach (var jsonString in GetJson())
			{
				var result = JsonConvert.DeserializeObject<JToken>(jsonString);
				
				var total = (string)result.SelectTokens("results.main[*].item.total").SingleOrDefault() ?? string.Empty;
				if (!string.IsNullOrEmpty(total))
				{
					// Process the total somehow.
				}
				Console.WriteLine(total);
			}
		}
		
        public static void Test1()
        {
			foreach (var jsonString in GetJson())
			{
				var result = JToken.Parse(jsonString);

				var total = (string)result.SelectToken("results.main[0].item.total") ?? string.Empty;
				if (!string.IsNullOrEmpty(total))
				{
					Console.WriteLine(total);
				}
				else
				{
					Console.WriteLine("no total");
				}
			}
		}	

        public static void Test2()
        {
			foreach (var jsonString in GetJson())
			{
				var result = JToken.Parse(jsonString);

				var items = result.SelectTokens("results.main[?(@.item.total)].item");
				foreach (var item in items)
				{
					var name = (string)item["name"];
					var total = (decimal)item["total"];
					Console.WriteLine("name = {0}, total = {1}", name, total);
				}
			}
		}	
		
		static IEnumerable<string> GetJson()
		{
			return new []
			{
				@"{
    ""results"": {
        ""copyright"": ""Copyright (c)"",
        ""main"": [{
            ""item"": {
                ""name"": ""fruit"",
                ""date"": ""1900-01-01"",
                ""total"": 123456
            }
        }]
    }
}
",
				@"{
    ""results"": {
        ""copyright"": ""Copyright (c)"",
        ""main"": [{
            ""item"": {
                ""name"": ""flubber"",
                ""date"": ""1900-01-01"",
            }
        }]
    }
}",
				
			};
		}
	}

	public class Program
	{
		public static void Main()
		{
			Console.WriteLine("Environment version: " + Environment.Version);
			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;
			}
		}
	}