Question

I am trying to call a POST API controller. The controller gets called but the complex object comes in empty. I have ran Fiddler and the object is even coming through populated there. What am I doing wrong?

My C# object

public class RegisterUser
{
    public Guid PersonId { get; set; }
    public string Email { get; set; }
    public string Business { get; set; }
    public string EmployeeNumber { get; set; }
    public string UserName { get; set; }
}

API Post Controller

public HttpResponseMessage Post(RegisterUser user)
{
   //This is where the problem is. Everything in user is null 
   //even though I can see it coming through on Fiddler.
}

Javascript code

function User(personId, userName, email, business, employeeNumber) {
   this.PersonId = personId;
   this.Email = email;
   this.Business = business;
   this.EmployeeNumber = employeeNumber;
   this.UserName = userName;
}

function RegisterUser(url) {
   var createdUser = new User("b3fd25ba-49e8-4247-9f23-a6bb90a62691", "username", "email", "business", "56465");
   $.ajax(url, {
       data: JSON.stringify({ user: createdUser }),
       type: "post",
       contentType: "application/json"
  });
}

Web API Route Config

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Routes.MapHttpRoute(
            name: "RegisterApi",
            routeTemplate: "api/{controller}/{user}"
        );
    }
}

Answer 1

createdUser already contains the data needed by Web.Api in the correct format there is no need to wrap it inside an user property which confuses the model binder.

Just write data: JSON.stringify(createdUser) and it should work fine:

function RegisterUser(url) {
   var createdUser = new User("b3fd25ba-49e8-4247-9f23-a6bb90a62691", "username", "email", "business", "56465");
   $.ajax(url, {
       data: JSON.stringify(createdUser),
       type: "post",
       contentType: "application/json"
  });
}

The principles of the model binding are simple until you have matching property names and object structure in your JS and C# objects and it should work fine.