Cascading dropdown lists MVC3

I have done something similar. Here is some of the code (apologies upfront for this being quite long, but I wanted to make sure you could re-create this on your side):

View looks like this:

using Cascading.Models
@model CascadingModel


@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Cascading Forms</h2>
<table>

@using(Html.BeginForm("Index", "Home"))
{
<tr>
    <td>@Html.LabelFor(m=>m.CategoryId)</td>
    <td>@Html.DropDownListFor(m => m.CategoryId, new SelectList(Model.Categories, "Id", "Name"), string.Empty)</td>
</tr>
<tr>
    <td>@Html.LabelFor(m=>m.ProductId)</td>
    <td>@Html.CascadingDropDownListFor(m => m.ProductId, new SelectList(Model.Products, "Id", "Name"), string.Empty, null, "CategoryId", "Home/CategorySelected")</td>
</tr>
<tr>
    <td>&nbsp;</td>
    <td><input type="submit" value="Go"/></td>
</tr>
}
</table>

the Model looks as follows:

public class CascadingModel
{
    public int CategoryId { get; set; }
    public List<Category> Categories { get; set; }
    public int ProductId { get; set; }
    public List<Product> Products { get; set; }
}

the real "clever" part of the system is the Html.CascadingDropDownListFor which looks as follows:

public static class MvcHtmlExtensions
{
    public static MvcHtmlString CascadingDropDownListFor<TModel, TProperty>(
        this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TProperty>> expression,
        IEnumerable<SelectListItem> selectList,
        string optionLabel,
        IDictionary<string, Object> htmlAttributes,
        string parentControlName,
        string childListUrl
        )
    {
        var memberName = GetMemberInfo(expression).Member.Name;

        MvcHtmlString returnHtml = Html.SelectExtensions.DropDownListFor(htmlHelper, expression, selectList, optionLabel, htmlAttributes);

        var returnString = MvcHtmlString.Create(returnHtml.ToString() + 
                    @"<script type=""text/javascript"">
                        $(document).ready(function () {
                            $(""#<<parentControlName>>"").change(function () { 
                                var postData = { <<parentControlName>>: $(""#<<parentControlName>>"").val() };
                                $.post('<<childListUrl>>', postData, function (data) {
                                    var options = """";
                                    $.each(data, function (index) {
                                        options += ""<option value='"" + data[index].Id + ""'>"" + data[index].Name + ""</option>"";
                                    });
                                    $(""#<<memberName>>"").html(options);
                                })
                                .error(function (jqXHR, textStatus, errorThrown) { alert(jqXHR.responseText); });
                            });
                        });
                     </script>"
                    .Replace("<<parentControlName>>", parentControlName)
                    .Replace("<<childListUrl>>", childListUrl)
                    .Replace("<<memberName>>", memberName));

        return returnString;

    }

    private static MemberExpression GetMemberInfo(Expression method)
    {
        LambdaExpression lambda = method as LambdaExpression;
        if (lambda == null)
            throw new ArgumentNullException("method");

        MemberExpression memberExpr = null;

        if (lambda.Body.NodeType == ExpressionType.Convert)
        {
            memberExpr = ((UnaryExpression)lambda.Body).Operand as MemberExpression;
        }
        else if (lambda.Body.NodeType == ExpressionType.MemberAccess)
        {
            memberExpr = lambda.Body as MemberExpression;
        }

        if (memberExpr == null)
            throw new ArgumentException("method");

        return memberExpr;
    }
}

Controller Logic for those looking for it:

public ActionResult CategoriesAndProducts()
{
    var viewModel = new CategoriesAndProductsViewModel();
    viewModel.Categories = FetchCategoriesFromDataBase();
    viewModel.Products = FetchProductsFromDataBase();
    viewModel.CategoryId = viewModel.Categories[0].CategoryId;
    viewModel.ProductId = viewModel.Products.Where(p => p.CategoryId).FirstOrDefault().ProductId;
    return View(viewModel);
}