Question

Why doesnt 3 level nesting model binding from json work?

Testing with 2 levels, say adding a string property on LevelTwo, works, but 3 levels doesnt? Is this by design, a bug, or am I missing something?

Client side jQuery post:

    $.ajax({
        url: "MyController/MyAction",
        dataType: "json",
        type: "POST",
        cache: false,
        data: {
            Level1: {
                Level2: {
                    StringValue: "Test"
                }
            }
        }
    });

Server side model:

public class MyForm
{
    public LevelOne Level1 { get; set; }
}

public class LevelOne
{
    public LevelTwo Level2 { get; set; }
}

public class LevelTwo
{
    public string StringValue { get; set; }
}

Answer 1

Why doesnt 3 level nesting model binding from json work

You are not sending any JSON to the server. If you want to send a JSON request here’s how:

$.ajax({
    url: "MyController/MyAction",
    contentType: 'application/json; charset=utf-8',
    dataType: "json",
    type: "POST",
    cache: false,
    data: JSON.stringify({ 
        Level1: { 
            Level2: { 
                StringValue: "Test" 
            } 
        } 
    })
});

The JSON.stringify method is what serializes the javascript literal into a JSON string. It is natively built in modern browsers. If you need to support legacy browsers you could include the json2.js script to your page.