Custom Validation for Cascading Dropdownlist in MVC Razor

public class MyViewModel
{
    public int SelectedCategoryId { get; set; }
    public IEnumerable Categories { get; set; } 
}

public ActionResult NewsEdit(int ID, dms_New dsn)
{
    var dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();

    var model = new MyViewModel
    {
        SelectedCategoryId = dsn.NewsCategoriesID,
        Categories = categories.Select(x => new SelectListItem
        {
            Value = x.NewsCategoriesID.ToString(),
            Text = x.NewsCategoriesName
        })
    };
    return View(model);
}

@model MyViewModel

@Html.DropDownListFor(
    x => x.SelectedCategoryId,
    Model.Categories
)  

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;
using System.Web.Mvc;
using System.Text.RegularExpressions;
 namespace Mvc4_Validate_CascadingDropdown.Models
 { 
public class RegistrationModel 
{
 [Required(ErrorMessage = "Please Enter Email Address")]
 [Display(Name = "UserName (Email Address)")]
 [RegularExpression(".+@.+\\..+", ErrorMessage = "Please Enter Correct Email Address")]
 public string UserName { get; set; }
 [Display(Name = "Country")]
 public Country Country { get; set; }
 [Display(Name = "City")]
 public City City { get; set; }
 [Required(ErrorMessage = "Please Enter Address")]
 [Display(Name = "Address")]
 [StringLength(200)]
 public string Address { get; set; }
 }
// IClientValidatable for client side Validation 
 public class MustBeSelectedAttribute : ValidationAttribute, IClientValidatable 
{
 public override bool IsValid(object value) {
 if (value == null || (int)value == 0)
 return false;
 else return true; 
} 
// Implement IClientValidatable for client side Validation 
public IEnumerable GetClientValidationRules(ModelMetadata metadata, ControllerContext context) 
{ 
return new ModelClientValidationRule[] 
{
 new ModelClientValidationRule { ValidationType = "dropdown", ErrorMessage = this.ErrorMessage } }; 
} 
}
 public class Country
 { 
[MustBeSelectedAttribute(ErrorMessage = "Please Select Country")] 
public int? ID { get; set; }
 public string Name { get; set; }
 }
 public class City 
{ 
[MustBeSelectedAttribute(ErrorMessage = "Please Select City")] 
public int? ID { get; set; } 
public string Name { get; set; }
 public int? Country { get; set; } 
}
} 

 @model Mvc4_Validate_CascadingDropdown.Models.RegistrationModel
@{ ViewBag.Title = "Validating Cascading Dropdownlist";
}
<script src="../../Scripts/jquery-1.7.1.min.js" type="text/javascript"></script>
<script src="../../Scripts/jquery.validate.min.js" type="text/javascript"></script>
<script src="../../Scripts/jquery.validate.unobtrusive.min.js" type="text/javascript"></script>
<script type="text/jscript">
 //Custom jQuery validation unobtrusive script and adapters 
jQuery.validator.unobtrusive.adapters.add("dropdown", function (options) {
 if (options.element.tagName.toUpperCase() == "SELECT" && options.element.type.toUpperCase() == "SELECT-ONE") {
 options.rules["required"] = true;
 if (options.message) {
 options.messages["required"] = options.message;
 }
 }
 });
 $(function () {
 //get city list on changing of country dropdown list 
$('#Country_ID').change(function () {
 var id = $("#Country_ID :selected").val();
 if (id != "") {
 $.ajax({
 type: "GET",
 contentType: "application/json; charset=utf-8",
 url: '@Url.Action("CityList", "Home")',
 data: { "mCountry": id },
 dataType: "json",
 beforeSend: function () {
 //alert(id); 
},
 success: function (data) {
 var items = "";
 $.each(data, function (i, city) {
 items += "<option value='" + city.Value + "'>" + city.Text + "</option>";
 });
 // Fill City Dropdown list 
$('#City_ID').html(items);
 },
 error: function (result) {
 alert('Service call failed: ' + result.status + ' Type :' + result.statusText);
 }
 });
 }
 else {
 var items = '<option value="">Select</option>';
 $('#City_ID').html(items);
 }
 });
 });
</script>
<h2>Custom Validation for Cascading Dropdown List</h2>
@using (Html.BeginForm())
{
 <fieldset> <legend>Custom Validation for Cascading Dropdown List</legend> 
<ol> <li> 
@Html.LabelFor(m => m.UserName) 
@Html.TextBoxFor(m => m.UserName, new { maxlength = 50 }) 
@Html.ValidationMessageFor(m => m.UserName) </li> 
<li> 
@Html.LabelFor(m => m.Country) 
@Html.DropDownListFor(m => m.Country.ID, new SelectList(ViewBag.Country, "ID", "Name", ViewBag.SelCountry), new { style = "width:310px" }) 
@Html.ValidationMessageFor(m => m.Country.ID) 
</li> 
<li> 
@Html.LabelFor(m => m.City) 
@Html.DropDownListFor(m => m.City.ID, new SelectList(ViewBag.City, "ID", "Name", ViewBag.SelCity), new { style = "width:310px" }) 
@Html.ValidationMessageFor(m => m.City.ID) 
</li> 
<li>
 @Html.LabelFor(m => m.Address)
 @Html.TextAreaFor(m => m.Address, new { maxlength = 200 }) 
@Html.ValidationMessageFor(m => m.Address) 
</li> 
</ol>
 <input type="submit" value="Submit" /> 
</fieldset>
 }   

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using Mvc4_Validate_CascadingDropdown.Models;
using System.Text.RegularExpressions;
namespace Mvc4_Validate_CascadingDropdown.Controllers {
 public class HomeController : Controller {
 #region Private Methods
 void BindCountry() {
 List<Country> lstCountry = new List<Country>
{
new Country { ID = null, Name = "Select" }, 
new Country { ID = 1, Name = "India" }, 
new Country { ID = 2, Name = "USA" } };
 ViewBag.Country = lstCountry;
 }
 //for server side
 void BindCity(int? mCountry) {
 try {
 if (mCountry != 0) 
{ 
//below code is only for demo, you can pick city from database
 int index = 1;
 List<City> lstCity = new List<City>{ 
new City { Country = 0, ID=null, Name = "Select" }, 
new City { Country = 1, ID=index++, Name = "Delhi" }, 
new City { Country = 1, ID=index++, Name = "Lucknow" }, 
new City { Country = 1, ID=index++, Name = "Noida" }, 
new City { Country = 1, ID=index++, Name = "Guragon" }, 
new City { Country = 1, ID=index++, Name = "Pune" }, 
new City { Country = 2, ID=index++, Name = "New-York" }, 
new City { Country = 2, ID=index++, Name = "California" },
 new City { Country = 2, ID=index++, Name = "Washington" }, 
new City { Country = 2, ID=index++, Name = "Vermont" }, };
 var city = from c in lstCity
 where c.Country == mCountry || c.Country == 0
 select c;
 ViewBag.City = city;
 }
 else {
 List<City> City = new List<City> { 
new City { ID = null, Name = "Select" } };
 ViewBag.City = City;
 }
 }
 catch (Exception ex) {
 }
 }
 #endregion
 //for client side using jquery
 public JsonResult CityList(int mCountry) {
 try {
 if (mCountry != 0) { 
//below code is only for demo, you can pick city from database
 int index = 1;
 List<City> lstCity = new List<City>{ 
new City { Country = 0, ID=null, Name = "Select" }, 
new City { Country = 1, ID=index++, Name = "Delhi" }, 
new City { Country = 1, ID=index++, Name = "Lucknow" }, 
new City { Country = 1, ID=index++, Name = "Noida" }, 
new City { Country = 1, ID=index++, Name = "Guragon" }, 
new City { Country = 1, ID=index++, Name = "Pune" }, 
new City { Country = 2, ID=index++, Name = "New-York" }, 
new City { Country = 2, ID=index++, Name = "California" }, 
new City { Country = 2, ID=index++, Name = "Washington" }, 
new City { Country = 2, ID=index++, Name = "Vermont" }, };
 var city = from c in lstCity
 where c.Country == mCountry || c.Country == 0
 select c;
 return Json(new SelectList(city.ToArray(), "ID", "Name"), JsonRequestBehavior.AllowGet);
 } 
}
 catch (Exception ex) {
 }
 return Json(null); 
}
 public ActionResult Index()
 {
 return View();
 }
 public ActionResult CustomDropdown()
 {
 BindCountry();
 BindCity(0);
 return View();
 }
 [HttpPost]
 public ActionResult CustomDropdown(RegistrationModel mRegister) 
{
 if (ModelState.IsValid) 
{
 return View("Completed");
 }
 else 
{
 ViewBag.SelCountry = mRegister.Country;
 BindCountry();
 ViewBag.SelCity = mRegister.City;
 if (mRegister.Country != null)
 BindCity(mRegister.Country.ID);
 else
 BindCity(null);
 return View(); 
}
 }
 }
}