Cascading Dropdownlist - Registering new Store

Hello,

In my project the company has a set of Stores where it operates. Each Store is located in a District and every District belongs to a Department (or city).

I'm trying to construct a view where I can show the Store properties (in a table) and I'm trying to add a cascading dropdownlist for the Departments and the Districts.

Here are the models so you can see the relationship between them:

Stores:

public class Store
{
[Key]
public int StoreID { get; set; }
[Display(Name = "Distrito")]
public int DistrictID { get; set; }
[Display(Name = "Cadena")]
public int StoreChainID { get; set; }
[Required]
[StringLength(60)]
[Display(Name = "Nombre")]
public string StoreName { get; set; }
[StringLength(60)]
[Display(Name = "Dirección")]
public string StoreAddress { get; set; }
[Display(Name = "Área")]
public int StoreArea { get; set; }
public virtual ICollection Machines { get; set; }
public virtual District Districts { get; set; }
public virtual StoreChain StoreChains { get; set; }
public virtual LocalExpenses LocalExpenses { get; set; }

District:

public class District
{
[Key]
public int DistrictID { get; set; }
public int DepartmentID { get; set; }
[StringLength(30)]
public string DistrictName { get; set; }
public virtual ICollection Stores{ get; set; }
public virtual Department Departments { get; set; }

Department:

public class Department
{
[Key]
public int DepartmentID { get; set; }
[StringLength(30)]
public string DepartmentName { get; set; }
[NotMapped]
public int DistrictID {get;set;}
public virtual ICollection Districts { get; set; }
}

In my Controller I have two actions for my Index. The first action populates the Index view (which has a table to show the stores) and gets the data for the list of Departments:

First action:

public async Task Index()
{
var plataformaContext = _context.Stores.Include(s => s.Districts).Include(c => c.StoreChains);
List departmentlist = new List();
//Getting the Data from DB
departmentlist = (from department in _context.Departments select department).ToList();
//Inserting an additional item into the list: The "Select"
departmentlist.Insert(0, new Department { DepartmentID = 0, DepartmentName = "Select" });
ViewBag.ListofDepartment = departmentlist;
return View(await plataformaContext.ToListAsync());
}

The second action is used to populate the dropdownlist:

[HttpPost]
public IActionResult Index(Department objdepartment, IFormCollection formCollection)
{
//Validación
if (objdepartment.DepartmentID == 0)
{
ModelState.AddModelError("", "Select Department");
}
else if (objdepartment.DistrictID == 0)
{
ModelState.AddModelError("", "Select District");
}
//Getting the selected value
var DistrictID = HttpContext.Request.Form["DistrictID"].ToString();
//Sending the data back to ViewBag after Posting Form
List departmentList = new List();
departmentList = (from department in _context.Departments
select department).ToList();
departmentList.Insert(0, new Department { DepartmentID = 0, DepartmentName = "Select" });
// Assigning departmentList to ViewBag
ViewBag.ListofDepartment = departmentList;
return View(objdepartment);
}

Finally, here is the Index view:

@model List
@{
ViewData["Title"] = "Index";
}
Index
"Create">Create New
class="table">
Nombre de Tienda @*@Html.DisplayNameFor(model => model.Stores.StoreName)*@
Address @*@Html.DisplayNameFor(model => model.Stores.StoreAddress)*@
Area @*@Html.DisplayNameFor(model => model.Stores.StoreArea)*@
Distrito @*@Html.DisplayNameFor(model => model.Stores.Districts)*@
Cadena @*@Html.DisplayNameFor(model => model.Stores.StoreChains)*@
@foreach (var item in Model) {
@Html.DisplayFor(modelItem => item.StoreName)
@Html.DisplayFor(modelItem => item.StoreAddress)
@Html.DisplayFor(modelItem => item.StoreArea)
@Html.DisplayFor(modelItem => item.Districts.DistrictID)
@Html.DisplayFor(modelItem => item.StoreChains.StoreChainID)
"Edit" asp-route-id="@item.StoreID">Edit |
"Details" asp-route-id="@item.StoreID">Details |
"Delete" asp-route-id="@item.StoreID">Delete
}
"StoresGlobal" asp-action="Index" method="post" class="form-horizontal" role="form">
class="form-group">
class="row">
class="alert-danger" aspp-validation-summary="ModelOnly">

class="col-xs-12 col-sm-6 col-md-6 col-lg-4">

for

="DepartmentName" class="control-label">

for

="DepartmentID"

class="form-control"

asp-items="@(new SelectList(ViewBag.ListofDepartment,"DepartmentID","DepartmentName"))">