jQuery AJAX post to MVC Controller object -- request shows up null

Question

I know I'm missing something in the details here.

Problem

Despite Googling, trying examples, different formats, etc, the AJAX request that I send always is validated as having all fields empty, but not being null.

I think I'm not sending things in the proper format for the controller to recognize it as an object but I'm not sure what.

Fiddler: What my request looks like

With some dummy data:

Code: Model Class

public class ContactUsMessage
{
    public string Email { get; set; }
    public string Name { get; set; }
    public string PhoneNumber { get; set; }
    public string Message { get; set; }
}

Code: WebAPI Controller

    [HttpPost]
    public HttpResponseMessage NewMessage(ContactUsMessage messageToSend)
    {
        if (messageToSend == null)
        {
            var sadResponse = Request.CreateResponse(HttpStatusCode.BadRequest, "Empty Request");
            return sadResponse;
        }

        var messageValidator = new ContactUsMessageValidator();
        var results = messageValidator.Validate(messageToSend);
        var failures = results.Errors;
        var sadString = "";
        if (!results.IsValid)
        {
            foreach (var error in failures)
            {
                sadString += " Problem: " + error.ErrorMessage;
            }
            var sadResponse = Request.CreateResponse(HttpStatusCode.NotAcceptable, "Model is invalid." + sadString);
            return sadResponse;

        }
        else
        {
            SendContactFormEmail(messageToSend.Email, messageToSend.Name, messageToSend.PhoneNumber, messageToSend.Message);

        }

Code: JavaScript on Page

function sendSubmissionForm() {

    var dataObject = JSON.stringify(
        {
            messageToSend: {
                'Email': $('#inpEmail').val(),
                'Name': $('#inpName').val(),
                'PhoneNumber': $('#inpPhone').val(),
                'Message': $('#inpMessage').val()
            }
        });

    $.ajax({
        url: '/api/contactus/newmessage',
        type: 'POST',
        done: submissionSucceeded,
        fail: submissionFailed,
        data: dataObject

    });


}

Solution

When you JSON.stringifyied your data object you converted it to JSON. But you forgot to set the Content-Type request header and the Web API has no way of knowing whether you are sending JSON, XML or something else:

$.ajax({
    url: '/api/contactus/newmessage',
    type: 'POST',
    contentType: 'application/json',
    done: submissionSucceeded,
    fail: submissionFailed,
    data: dataObject
});

Also when building the JSON you don't need to wrap it in an additional property that matches your method argument name. The following should work as well:

var dataObject = JSON.stringify({
    'Email': $('#inpEmail').val(),
    'Name': $('#inpName').val(),
    'PhoneNumber': $('#inpPhone').val(),
    'Message': $('#inpMessage').val()
});