how to display selected checkbox as checked in another edit action page mvc razor

In my Create action I have given many checkbox for selecting items for eg, suppose I have 5 checkbox items and I selected 3 out of that and these selected checkboxes are stored in db and here my problem is, from the index page when I click on the edit link I want to list the entire checkbox items ie, 5 and also want to show the checked checkbox as checked in edit page ie, the 3 items that is checked, so that the user can change the selected checkbox and these changed items must add to db

controller

 // GET: MappedName/Edit/5
    public async Task<ActionResult> Edit(int? id )
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        MappedName mappedName= await db.MappedNames.FindAsync(id);

        var ListItems = (from ap in db.MappedNames
                         join a in db.Masters on ap.MasterId equals a.ID
                         join p in db.Posts on ap.PostId equals p.Id
                         select new MappingList
                         {
                             id = ap.Id,
                             Masterid = ap.MasterId,
                             postid = ap.PostId,
                             firstname = a.FirstName,
                             Postname = p.PostName
                         }).Where(r=>r.Masterid == id).ToList();

        var grp = ListItems.GroupBy(r => r.Masterid).Select(r => new MappingList
        {
            Masterid = r.Key,
            id = r.Key,
            PostNames = string.Join(" , ", r.Select(g => g.Postname)),
            firstname = ListItems.FirstOrDefault(q => q.Masterid == r.Key).firstname
        }).FirstOrDefault();

        string combindedString = string.Join(",", mappedName.GetAllSelctedCheckBoxes.ToArray());

        MappedName mappedNames= new MappedName();
        {
            mappedNames.Id = grp.id.Value;
            mappedNames.MasterId = grp.Masterid;

        }


        var m = db.Masters.Where(r => r.ID == id).Select(p=>p.FirstName);
        ViewBag.MasterId = new SelectList(m,  "FirstName");
        ViewBag.DistrictId = new SelectList(db.DistrictMasters, "Id", "DistrictName");


        if (mappedNames== null)
        {
            return HttpNotFound();
        }
        return View(mappedNames);
    }

 [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> Edit(MappedName mappedName)
    {
        string combindedString = string.Join(",", mappedName.GetAllSelctedCheckBoxes.ToArray());
        List<int> check = new List<int>(combindedString.Split(',').Select(int.Parse));

        if (ModelState.IsValid)
        {
            for (int i = 0; i < check.Count(); i++)
            {
                mappedName.PostId = Convert.ToInt32(check[i]);
                mappedName.PostId = mappedName.PostId;
                mappedName.MasterId = mappedName.MasterId;
                db.MappedNames.Add(mappedName);
                await db.SaveChangesAsync();
            }
            //db.Entry(mappedName).State = EntityState.Modified;
            //await db.SaveChangesAsync();
            return RedirectToAction("Index");
        }
        return View(mappedName);
    }

this is my edit action of httpget and httppost

view

@model A.Models.MappedName 

     <div class="form-group">
            @Html.LabelFor(model => model.PostId, "PostName", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                <div id="PostMaster"></div>
                @Html.HiddenFor(m => m.GetAllSelctedCheckBoxes)

                @Html.ValidationMessageFor(model => model.PostId, "", new { @class = "text-danger" })

  <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </div>
    </div>


 <script>
    $("#Create").click(function () {
        $('#GetAllSelctedCheckBoxes').empty();
        debugger;
        var getList = [];
        $("#PostMaster input:checked").each(function () {
            getList.push($(this).val());
        });
        $('#GetAllSelctedCheckBoxes').val(getList);// assign to hidden field
    });
</script> 

Here in this GetAllSelctedCheckBoxes I am getting all the selected checkbox items

model

 public partial class MappedName
{
    public int Id { get; set; }
    public Nullable<int> MasterId { get; set; }
    public Nullable<int> PostId { get; set; }
    public List<string> GetAllSelctedCheckBoxes { get; set; }
}

Here the GetAllSelctedCheckBoxes is not bind to db and is written in model class My Problem is that I need to show the selected checkbox as check when I click on the edit link and need to save the edited checked box if any change occurs for eg, adding one more checkbox ? how can I do that ?can anyone please help me to find the solution ??