MVC Deserializes null into "null" (string)

Question

I'm passing an object from jQuery to a MVC3 Controller via a $.ajax POST. While debugging using Developer Tools, I can see the object I'm assigning to the ajax data property. The object contains properties whose value is null. When I debug the Controller, the properties which were null in the JS Debugger are now "null" (strings).

Why is this? What can I do to prevent this from happening?

C# Object

public class User
{
   public string Name { get; set; }
}

Javascript Object

var user = {
Name: null
}

Controller Method

public JsonResult HelloWorld(User user) { .. some logic .. }

ajax Call

var data = user;
$.ajax({
url: '/Controller/HelloWorld/',
data: data,
type: 'post',
success: ...
error: ...
})

We aren't doing anything special. Create a c# object, create a javascript object which matches (leaving some properties as null), then use jQuery ajax to POST that object to a Controller method. The object is coming over with the properties as "null" so the logic within the Controller method doesn't matter. — Mark Meisel, Jun 28 '12 at 19:07
cool, can you show *how* you're doing that `POST` in JavaScript then? — MilkyWayJoe, Jun 28 '12 at 19:10
honest question. Have you tried specifying `contentType: 'application/json; charset=utf-8'`? (not 100% sure if it helps in this case tho) — MilkyWayJoe, Jun 28 '12 at 19:17
@LeeGunn you *are* missing something. It's `null` in js, but it's `string` in cs (with the value of null) — MilkyWayJoe, Jun 28 '12 at 19:18
Have a look at the accepted answer in [this](http://stackoverflow.com/questions/8448150/asp-net-mvc-receives-null-as-a-string-instead-of-null) link — MilkyWayJoe, Jun 28 '12 at 19:25

score 4 · Accepted Answer · answered Jun 28 '12 at 19:52

4

Yeap, that's an unfortunate side effect with the default model binder. You could avoid it by either not including null properties in the request at all or by using a JSON request:

$.ajax({
    url: '@Url.Action("HelloWorld", "Controller")',
    data: JSON.stringify({ Name: null }),
    contentType: 'application/json',
    type: 'post',
    success: function (result) {
        // ...
    }
});

Things to notice:

contentType: 'application/json'.
JSON.stringify around the data parameter in order to convert to a JSON string the request.

answered Jun 28 '12 at 19:52

Darin Dimitrov

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so it turns out `contentType` helps a little in this case after all – MilkyWayJoe Jun 28 '12 at 19:55
Yes it helps because it is now the JSON value provider factory using the JavaScriptDeserializer class which handles the parsing instead of the default model binder. – Darin Dimitrov Jun 28 '12 at 19:56
yeah, I suggested that but the OP never replied. As for the `null`-"null" issue, I recommended the approach in a different question but `JSON.stringify` is definitely the way to go, so you don't have to check each individual property... +1 – MilkyWayJoe Jun 28 '12 at 19:59

MVC Deserializes null into "null" (string)

1 Answers1