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/78185962/net-json-property-custom-required-logic

​

    public class Foo

    {

        [JsonProperty(Required = Required.Always)]

        public int Number { get; set; }

​

        public string Text { get; set; }

        [System.Runtime.Serialization.OnDeserialized]

        void OnDeserializedMethod(System.Runtime.Serialization.StreamingContext context)

        {

            if (Number > 10 && Text == null)

            {

                throw new JsonSerializationException("missing text");

            }

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            Assert.DoesNotThrow(() => JsonConvert.DeserializeObject<Foo>("""{ "Number": 5 }"""));

            Assert.That(() => JsonConvert.DeserializeObject<Foo>("""{ "Number": 20 }"""), Throws.Exception);

            Assert.DoesNotThrow(() => JsonConvert.DeserializeObject<Foo>("""{ "Number": 20, "Text": "Bar" }"""));

            Assert.That(() => JsonConvert.DeserializeObject<Foo>("""{ "Number": 20, "Text" : null }"""), Throws.Exception);

        }   

    }

​

    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;

            }

        }

    }

​