Why drop down branch cleared after return search result?

Question

I work on razor asp.net . I face issue drop down branch reset after return search result based on drop down branch .

I expect to still have same value I get the result based on it .

so why it cleared

Exactly I need selected branch i search by it still exist after click search result and return data .

  <form id="FrmShelfLabelPrintrSetup" method="post" onsubmit="return validateForm() ">

            <div class="row">
                <div class="col-lg-12 col-12 row">
                    <div class="col-md-3 col-lg-2">
                        <label for="branch-selectlbl" style="margin-left:3px;font-size:15px;font-family: 'Open Sans', sans-serif;font-weight: bold;">Print Server</label>
                  
                        <select id="branch-select" asp-for="SelectedBranchId" name="selectbranchid" class="form-select" style="margin-left:3px;font-size:15px;font-family: 'Open Sans' , sans-serif;font-weight: bold;" onchange="toggleButtonVisibility()">
                            <option value="0">--Select--</option>
                            @foreach (var branches in Model.branches)
                            {

                                <option value="@branches.iBranchCode">@branches.vBranchDesc</option>


                            }
                        </select>
                       
                    </div>

                    <div class="col-md-3 col-lg-2">
                        <br>
                        <button  id="Searchtxt" type="submit" name="searchButton" value="search" asp-page-handler="Search" style="width:100px;margin-top:7px;" class="btn btn-primary">Search</button>
                       

                    </div>

                    
                </div>
            </div>







        </form>

    </div>

 public async Task<IActionResult> OnPostSearchAsync(string selectbranchid)
        {
            
            DataTable dtresults =  _IAdcSupportService.ExecuteQuery(_IAdcSupportService.GetAllPrinters("Branch", selectbranchid));
            if(dtresults.Rows.Count>0)
            {
                ViewData["SearchResults"] = dtresults;
            }
          
         
            
            DataTable dtbranches = _IAdcSupportService.GetBranchDetails();
            branches = dtbranches.AsEnumerable()
 .Select(row => new UC.ADC.Core.Entities.SQL.Branch
 {

     iBranchCode = (string)row["iBranchCode"],
     vBranchDesc = row["vBranchDesc"].ToString()
    
 })
 .ToList();
            

            return Page();
        }

Answer 1

You can add a nullable attribute to the Branch model to determine whether it is selected, and add [NotMapped] to it to prevent it from matching in the database.

[NotMapped]
public bool? Selected { get; set; }

OnPostSearchAsync:

branches = dtbranches.AsEnumerable()
 .Select(row => new UC.ADC.Core.Entities.SQL.Branch
 {

    iBranchCode = (string)row["iBranchCode"],
    vBranchDesc = row["vBranchDesc"].ToString(),
    // add this line
    Selected = ((string)row["iBranchCode"] == selectbranchid)? true: null

 })
 .ToList();

And in your form:

@foreach (var branches in Model.branches)
{
     string selected = null;
     @if(branches.Selected == true)
     {
         selected = "selected";
     }
     <option selected=@selected value="@branches.iBranchCode">@branches.vBranchDesc</option>
}