Serializing to JSON, Nullable Date gets omitted using Json.NET and Web API despite specifying NullValueHandling

Question

using Newtonsoft.Json;

namespace FAL.WebAPI2012.Controllers
{
    public class Person
    {
        public int Id {get;set;}
        public string FirstName {get;set;}
        public string LastName {get;set;}

        [JsonProperty(DefaultValueHandling = DefaultValueHandling.Include, 
            NullValueHandling = NullValueHandling.Include)]
        public DateTime? Dob { get; set; }
    }

    public class TestNullsController : ApiController
    {
        // GET api/<controller>
        public Person Get()
        {
            Person myPerson = new Person() { 
                Dob = null, FirstName = "Adrian", Id=1, LastName="Bobby"
            };

            return myPerson;
        }
    }
}

As you can see, my Dob field is set to null but the result is the following

{ "Id":1, "FirstName":"Adrian", "LastName":"Bobby" }

and Dob is not serialized to null which I need it to be!

(I have tested that JsonProperty is setting other attributes like name and it changes the JSON output perfectly. I just can't get the nullable property to be serialized. Also, I have tested Json.Net (see answer below), so my thinking is that web api setup is overriding something somewhere, would be nice to know where).

Answer 1

It would appear that the problem lies somewhere else. I've done the following in a console application:

using System;
using System.IO;
using Newtonsoft.Json;

namespace JsonNetNullablePropertyTest
{
    class Program
    {
        static void Main()
        {
            var myPerson = new Person {
                Dob = null,
                FirstName = "Adrian",
                Id = 1,
                LastName = "Bobby"
            };

            using (var textWriter = new StringWriter())
            using (var writer = new JsonTextWriter(textWriter))
            {
                // Create the serializer.
                var serializer = new JsonSerializer();

                // Serialize.
                serializer.Serialize(writer, myPerson);

                // Write the output.
                Console.WriteLine(textWriter);
            }
        }
    }

    public class Person
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }

        [JsonProperty(DefaultValueHandling = DefaultValueHandling.Include,
            NullValueHandling = NullValueHandling.Include)]
        public DateTime? Dob { get; set; }
    }
}

And the output is:

{"Id":1,"FirstName":"Adrian","LastName":"Bobby","Dob":null}

As expected.

It would seem that the problem lies in how you are actually calling the JsonSerializer to serialize the Person instance.

Answer 2

I received this reply from a member of the web.api folk at Microsoft.

'You'll be glad to know this has been fixed since RC:

http://aspnetwebstack.codeplex.com/workitem/243

You can either upgrade to a newer package, or you can override our settings like this:

JsonFormatter.SerializerSettings = new JsonSerializerSettings() { NullValueHandling = NullValueHandling.Include };

Hope that helps'

So, all works with that update.