Как восстановить старое изображение Path, когда мы не обновляем c# mvc

Question

Я работаю над формой обновления, мой сценарий - я не хочу обновлять новое изображение. Я просто хочу обновить только другие данные, а затем отправить, когда я отправляю форму. «URL изображения» показывает нулевое значение, а не старый путь. я попробовал этот код, которым я делюсь, пожалуйста, скажите мне, как решить эту проблему. Просто дайте намек на код, и я разрешу это.

Модель

  public class ProductViewModel{

        public string ImageUrl { get; set; }  

        [NotMapped]  
        public HttpPostedFileBase imageUpload { get; set; }  

        public ProductViewModel()  
        {  
            ImageUrl = "~/Scripts/imageloading/image.jpg";  
        }  
} 

c#

  public ActionResult AddOrEditProducts(ProductViewModel prod)  
           {  
               Product pro = new Product();  
               ProductDetail p_spec = new ProductDetail();  
               var result = new jsonMessage();  
               try  
               {  
                   List<ProductType> PTlist = _IproductType.PTList();  
                   ViewBag.Ptlist = new SelectList(PTlist, "PType_ID", "P_Name");  

                   //Product Color List  
                   List<P_Color> pColorList = _IProductColor.PColorlist();  
                   ViewBag.pColor_List = new SelectList(pColorList, "C_ID", "C_Name_OR_Code");  

                   List<P_Size> pSizeList = _ISize.pSizeList();  
                   ViewBag.pSizeLists = new SelectList(pSizeList, "S_ID", "S_Size");  

                   if (prod.imageUpload != null)  // shows null here
                   {  
                           string filename = Path.GetFileName(prod.imageUpload.FileName);  
                           string _filename = DateTime.Now.ToString("yymmssff") + filename;  
                           string extension = Path.GetExtension(prod.imageUpload.FileName);  
                           prod.ImageUrl= "~/upload/" + _filename;  
                       if (extension.ToLower() == ".jpeg" || extension.ToLower() == ".jpg" || extension.ToLower() == ".png")  
                           {  
                               if (prod.imageUpload.ContentLength <= 1000000)  
                               {  
                                   prod.imageUpload.SaveAs(Path.Combine(Server.MapPath("~/upload/"), _filename));
                                   p_spec = new ProductDetail();  
                                   p_spec.ProductID = prod.ProductID;  
                                   p_spec.OS = prod.OS.Trim();  
                                   p_spec.DualSim = prod.DualSim.Trim();  
                                   p_spec.Camera = prod.Camera.Trim();  
                                   p_spec.TouchScreen = prod.TouchScreen.Trim();  
                                   p_spec.ScreenSize = prod.ScreenSize.Trim();  
                                   p_spec.ProcessorType = prod.ProcessorType.Trim();  
                                   p_spec.RAM = prod.RAM.Trim();  
                                   p_spec.InternalMemory = prod.InternalMemory.Trim();  
                                   p_spec.Wifi = prod.Wifi.Trim();  
                                   p_spec.BatteryLife = prod.BatteryLife.Trim();  
                                   p_spec.Other = prod.Other.Trim();  
                                   p_spec.PDescription = prod.PDescription.Trim();  
                                   p_spec.Model = prod.Model.Trim();  
                                   p_spec.Condition = prod.Condition.Trim();  
                                   p_spec.Discount = prod.Discount;  
                                   p_spec.ImageUrl = prod.ImageUrl;  

                               }  
                               else  
                                   ViewBag.sizemsg = "Size Limit accessed ";  
                           }  
                           else  
                               ViewBag.fileformat = "File is not Format is not Correct";  

                       pro = new Product();  
                       pro.ProductID = prod.ProductID;  
                       pro.PName = prod.PName.Trim();  
                       pro.ManificturedPrice = prod.ManificturedPrice;  
                       pro.P_SizeID = prod.P_SizeID;  
                       pro.P_Color_ID = prod.P_Color_ID;  
                       pro.PType_ID = prod.PType_ID;  
                       pro.UnitWeight = prod.UnitWeight;  
                       pro.UnitInStock = prod.UnitInStock;  
                   }  

                   if (prod.ProductID == 0)  
                   {  
                       _IProducts.AddOrEditProducts(pro, p_spec);  
                       result.Message= "Product has been saved success..";  
                       result.Status = true;  
                       ModelState.Clear();  
                   }  
                   else  
                   {  
                       _IProducts.AddOrEditProducts(pro, p_spec);  
                       result.Message = "Product Update Successfully";  
                       result.Status = true;  
                       ModelState.Clear();  
                   }  
               }  
               catch (DbEntityValidationException e)  
               {  
                   foreach (var eve in e.EntityValidationErrors)  
                   {  
                       Console.WriteLine("Entity of type \"{0}\" in state \"{1}\" has the following validation errors:",  
                           eve.Entry.Entity.GetType().Name, eve.Entry.State);  
                       foreach (var ve in eve.ValidationErrors)  
                       {  
                           Console.WriteLine("- Property: \"{0}\", Error: \"{1}\"",  
                               ve.PropertyName, ve.ErrorMessage);  
                       }  
                       result.Message = "We are unable to process your request at this time. Please try again later.";  
                       result.Status = false;  
                   }  
               }  
               return RedirectToAction("ProductsList");  
           }  

Вид

<div id="tabimage" class="tab-pane">  
                           <h3 class="mgtp-15 mgbt-xs-20"> Images</h3>  
                           <div class="vd_panel-menu">  

                               <input type="submit" value="Save Changes" class="btn vd_btn vd_bg-blue btn-icon btn-sm save-btn  fa fa-save" id="btnSave" />  
                               <button type="reset" value="Cancel" class="btn vd_btn vd_bg-blue btn-icon btn-sm save-btn  fa fa-save" id="" />  

                           </div>  
                           <div class="row">  
                               <div class="form-group">  
                                   <label class="control-label col-lg-3 file_upload_label"> <span title="" data-toggle="tooltip" class="label-tooltip" data-original-title="Format JPG, GIF, PNG. Filesize 8.00 MB max."> Add a new image to this product </span> </label>  
                                   <div class="col-lg-9">  
                                       <div class="col-lg-5">  
                                           <span class="btn vd_btn vd_bg-green fileinput-button">  
                                               <i class="glyphicon glyphicon-plus"></i> <span>Add files...</span>  
                                               <input type="file" name="imageUpload" multiple id="imageUpload" onchange="ShowimahePreview(this,document.getElementById('previewImage'))" />  
                                           </span>  
                                       </div>  

                                       <div class="col-lg-4">  
                                           <img src="@Url.Content(Model.ImageUrl)" alt="Alternate Text" height="150" weight="" id="previewImage" />  
                                       </div>  

                                   </div>  
                               </div>  


                           </div>  

                       </div>