Question

I’m new with MVC3 framework. So I was practicing and trying to learn how to have a Cascading dropdownlist using jquery. And I found this sample by Rick Anderson: http://blogs.msdn.com/b/rickandy/archive/2012/01/09/cascasding-dropdownlist-in-asp-net-mvc.aspx

So I tried to customize my own website with this sample in order to have a cascading dropdownlist. Here is my controller:

private SelectList GetMakeSelectList()
    {
        var makeQry = from m in db.Car
                      orderby m.Make
                      select m.Make;
        return new SelectList(makeQry.ToArray(), "Make");
    }

    public ActionResult MakeList()
    {
        if (HttpContext.Request.IsAjaxRequest())
            return Json(GetMakeSelectList(), JsonRequestBehavior.AllowGet);

        return RedirectToAction("Categories");
    }

    public ActionResult ModelList(string Make)
    {
        string make = Make;
        var model = from s in db.Car
                     where s.Make == make
                     select s.Model;

        if (HttpContext.Request.IsAjaxRequest())
            return Json(new SelectList(
                            model.ToArray())
                       , JsonRequestBehavior.AllowGet);

        return RedirectToAction("Categories");
    }

    public ActionResult Categories()
    {
        return View();
    }

and here is my model:

public class Car
{
    public int ID { get; set; }

    public String Make { get; set; }

    public String Model { get; set; }

    public decimal Price { get; set; }

    public String Edition { get; set; }

    public String Type { get; set; }

    public decimal Consumption { get; set; }

    public decimal Acceleration { get; set; }

    public decimal Horsepower { get; set; }

    public bool? Convertible { get; set; }
}
public class MovieDBContext : DbContext
{
    public DbSet<Car> Car { get; set; }
}

The problem is: String Make in ModelList method is null.
So I’m trying to not set my values manually in model class but set them just in the database.

My guess is: that the SelectList(makeQry.ToArray(), “Make”), the selected value’s type that I’m using is not what it expects to be. But I have no idea how to pass the expected type for a query.

And I’m using Jquery for this.
I would really appreciate any help.

Update:
Here is the View:

@model IEnumerable<Cars.Models.Car>

<script src="@Url.Content("~/Scripts/GetMake.js")"></script>
<script src="@Url.Content("~/Scripts/makeModel.js")"></script>
<link rel="stylesheet" type="text/css" href="@Url.Content("~/Content/CategoriesStyle.css")" />

@using (Html.BeginForm("Categories", "Category", FormMethod.Post, 
new { id = "CategoryFormID", 
    data_modelListAction = @Url.Action("ModelList"),
    data_makeListAction = @Url.Action("MakeList")})) {

<div id="content">
    <fieldset>
        <legend>Advanced Search</legend> 

        <div class="myform">

            <p>Search the car you're looking for in all details you can imagine right here!</p>

            <div id="MakeDivID">
                <label>Make</label>
                <select id="MakeID" name="Make"></select>
            </div>

            <div id="ModelDivID">
                <label>Model</label>
                <select id="ModelID" name="Model"></select>
            </div>



            <button type="submit" id="SubmitID">Search</button>
        </div>
    </fieldset>
</div>

}

and this would be my Jquery where I fill the dropboxes and call the methods:

this is GetMake.js

$(function () {
var URL = $('#CategoryFormID').data('makeListAction');
$.getJSON(URL, function (data) {
    var items = "<option>Select a Car Make</option>";
    $.each(data, function (i, make) {
        if (make.Text.indexOf("\'") > -1) {
            s = make.Text;
            alert(s + ": Country.Value cannot contain \'")
        }
        items += "<option>" + make.Text + "</option>";
    });
    $('#MakeID').html(items);
});
});

and this is makeModel.js:

$(function () {
$('#ModelDivID').hide();
$('#SubmitID').hide();
$('#MakeID').change(function () {
    var URL = $('#CategoryFormID').data('modelListAction');
    $.getJSON(URL + '/' + $('#MakeID').val(), function (data) {
        var items = '<option>Select a Model</option>';
        $.each(data, function (i, model) {
            items += "<option>" + model.Text + "</option>";
            // state.Value cannot contain ' character. We are OK because state.Value = cnt++;
        });
        $('#ModelID').html(items);
        $('#ModelDivID').show();
    });
});
$('#ModelID').change(function () {
    $('#SubmitID').show();
});
});

Second Update:
I forgot the mention the result that I get which is not what I’m looking for.
The result is that the first dropbox appears with all the correct values inside, when I click one of them, the second dropbox appears but it’s empty since I’m not passing the Make object is null in ModelList().

Third Update:
here is my routing as you asked. I hope this is what you were looking for.

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;

namespace Cars
{
// Note: For instructions on enabling IIS6 or IIS7 classic mode, 
// visit http://go.microsoft.com/?LinkId=9394801

public class MvcApplication : System.Web.HttpApplication
{
    public static void RegisterGlobalFilters(GlobalFilterCollection filters)
    {
        filters.Add(new HandleErrorAttribute());
    }

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            "Default", // Route name
            "{controller}/{action}/{id}", // URL with parameters
            new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
        );

    }

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        // Use LocalDB for Entity Framework by default
        Database.DefaultConnectionFactory = new SqlConnectionFactory(@"Data Source=(localdb)\v11.0; Integrated Security=True; MultipleActiveResultSets=True");

        RegisterGlobalFilters(GlobalFilters.Filters);
        RegisterRoutes(RouteTable.Routes);
    }
}
}

Answer 1

Having seen your routes, I think this is your issue:

public ActionResult ModelList(string Make)

Your routes say that the parameter must be called id, so that it can be mapped (this is the default routing.. which is why I wanted to double check).

routes.MapRoute(
        "Default", // Route name
        "{controller}/{action}/{id}", // <---- This part here says {id}
        new { controller = "Home", action = "Index", id = UrlParameter.Optional }
    );

To fix your issue, you probably only need to change the ModelList function to be this:

public ActionResult ModelList(string id) {
    string make = id; // assign the string id to the make variable