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 Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

using Newtonsoft.Json.Schema;

​

// https://stackoverflow.com/questions/47947461/validate-object-against-a-schema-before-serialization

    public static class JsonExtensions

    {

        public static bool TestValidate<T>(T obj, JSchema schema, SchemaValidationEventHandler handler = null, JsonSerializerSettings settings = null)

        {

            using (var writer = new NullJsonWriter())

            using (var validatingWriter = new JSchemaValidatingWriter(writer) { Schema = schema })

            {

                int count = 0;

                if (handler != null)

                    validatingWriter.ValidationEventHandler += handler;

                validatingWriter.ValidationEventHandler += (o, a) => count++;

                JsonSerializer.CreateDefault(settings).Serialize(validatingWriter, obj);

                return count == 0;

            }

        }

    }

​

    // Used to enable Json.NET to traverse an object hierarchy without actually writing any data.

    class NullJsonWriter : JsonWriter

    {

        public NullJsonWriter()

            : base()

        {

        }

        public override void Flush()

        {

            // Do nothing.

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            // Example adapted from 

            // https://www.newtonsoft.com/jsonschema/help/html/JsonValidatingWriterAndSerializer.htm

            // by James Newton-King

            string schemaJson = @"{

               'description': 'A person',

               'type': 'object',

               'properties': {

                 'name': {'type':'string'},

                 'hobbies': {

                   'type': 'array',

                   'maxItems': 3,

                   'items': {'type':'string'}

                 }

              }

            }";         

            var schema = JSchema.Parse(schemaJson);

            var person = new

            {

                Name = "James",

                Hobbies = new [] { ".Net", "Blogging", "Reading", "XBox", "LOLCATS" },

            };

            var settings = new JsonSerializerSettings { ContractResolver = new CamelCasePropertyNamesContractResolver() };

            var isValid = JsonExtensions.TestValidate(person, schema, (o, a) => Console.WriteLine(a.Message), settings);

            // Prints Array item count 5 exceeds maximum count of 3. Path 'hobbies'.

            Console.WriteLine("isValid = {0}", isValid); 

            // Prints isValid = False

        }

    }

​

    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;

            }

        }

    }

​

    public class AssertionFailedException : System.Exception

    {

        public AssertionFailedException() : base() { }

​

        public AssertionFailedException(string s) : base(s) { }

    }

​

    public static class Assert

    {

        public static void IsTrue(bool value)

        {

            IsTrue(value, "failed");

        }

​

        public static void IsTrue(bool value, string message)

        {

            if (value == false)

                throw new AssertionFailedException(message ?? "failed");

        }

    }

​