select item from city not fill items in district drop down

I have 4 table relation in sql server database is good

Country table

Id primarykey increment identity

Countryname

City table

Id primary key increment identity

Cityname

CountryId forignkey

Ditrict table

Id primarykey increment identity

Districtname

CityId forignkey

Employee table

Id primary key increment identity

fname

sname

salary

Bonus

districtid forignkey

Relation not have any proplem

when select items from country it fill city drop down list without any problem

but when i select item from city it not fill items in district why

something wrong in my code i do as following

my controller employee as following

EmployeeController

public class EmployeeController : Controller  
{  
  
// GET: Employee  
mytaskdbEntities db = new mytaskdbEntities();  
public ActionResult Index()  
{  
return View(db.Employees.ToList());  
}  
public ActionResult Create()  
{  
ViewBag.CountryList = new SelectList(db.Countries.ToList(), "Id","Countryname");  
  
return View();  
}  
public JsonResult getcitybyid(int id)  
{  
db.Configuration.ProxyCreationEnabled = false;  
return Json(db.Cities.Where(a =>a.CountryId == id), JsonRequestBehavior.AllowGet);  
}  
public JsonResult getdistrictbyid(int id)  
{  
db.Configuration.ProxyCreationEnabled = false;  
return Json(db.Districts.Where(a => a.CityId == id), JsonRequestBehavior.AllowGet);  
}  
}  
}