DropDownList selected value returns null in the Model on form POST in ASP.Net MVC

Hello everyone

When I try this part of code in my View - It works fine with my js code

<div class="form-group">
    @Html.LabelFor(model => model.PositionId, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownListFor(model => model.PositionId, new SelectList(" "), "--Select Position--", new { @class = "form-control" })
        @Html.ValidationMessageFor(model => model.PositionId, "", new { @class = "text-danger" })
    </div>
</div>

<script>
    $(document).ready(function () {
        $("#DepartmentId").change(function () {
            $.get("/Insertion/GetPositionList", { DepartmentId: $("#DepartmentId").val() }, function (data) {
                $("#PositionId").empty();
                $.each(data, function (index, row) {
                    $("#PositionId").append("<option value='" + row.PositionId + "'>" + row.PositionName + "</option>")
                });
            });
        })
    });
</script>

But when I try to write in my database my result of input from my web form I have troubles and null values instead in my database

So I need to write my code like this

To have in my database values of name of selected position

<div class="form-group">
    @Html.LabelFor(model => model.PositionName, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownListFor(model => model.PositionName, new SelectList(" "), "--Select Position--", new { @class = "form-control" })
        @Html.ValidationMessageFor(model => model.PositionName, "", new { @class = "text-danger" })
    </div>
</div>

But my dropdownlist doesnot work properly....Because there is no value of names of positions...

My controller works like this

[HttpPost]
public ActionResult Load(ViewModel model)
{
DBEntities db = new DBEntities();

Department dep = new Department();
dep.DepartmentId = model.DepartmentId;
dep.DepartmentName = model.DepartmentName;

DepPosition pos = new DepPosition();
pos.PositionId = model.PositionId;
//pos.PositionName = model.PositionName;

Gender gen = new Gender();
gen.GenderId = model.GenderId;
gen.GenderName = model.GenderName;


int latestEmpId = dep.DepartmentId;

Incentive inc = new Incentive();
inc.IncentiveAmount = model.IncentiveAmount;
inc.IncentiveId = model.IncentiveId;

Employee emp = new Employee();
emp.Name = model.Name;
emp.Gender = model.GenderName;
emp.Age = model.Age;
emp.Position = model.PositionName;
emp.Salary = model.Salary;
emp.HireDate = model.HireDate;
emp.Department_Id = model.DepartmentId;
emp.Incentive_Id = model.IncentiveId;
db.Employees.Add(emp);
db.SaveChanges();


ModelState.Clear();

ViewBag.SuccessMessage = "Информация добавлена автоматически";
return View("Load", new ViewModel());

}


{
db.Configuration.ProxyCreationEnabled = false;
List<DepPosition> PositionList = db.DepPositions.Where(x => x.Department_Id == DepartmentId).ToList();
return Json(PositionList, JsonRequestBehavior.AllowGet);
}

How it possible to write js code or controller code to have data in ddlist and have no problem writing it in database?