C#

[DataMember]
public ServiceArm ServiceArm { get; set; } = ServiceArm.Undefined;

public string ServiceName => Enum.GetName( typeof( ServiceArm ), this.ServiceArm );

block.ServiceArm = Enum.Parse<ServiceArm>( unit.ServiceName );

[HttpGet]    
public ActionResult ExportSummaryToExcel(string startDate, string endDate, string postalCode)
{
    string strStartDate = startDate;
    string strEndDate = endDate;
    string strRequestedPostalCode = postalCode;

    ViewBag.StartDate = startDate;
    ViewBag.EndDate = endDate;
    ViewBag.RequestedPostalCode = postalCode;

    DataTable rsReportDataByPostalCode = _summaryByAgeStagePostalCodeService.
        GetSummaryByPostalCode(strStartDate + " 00:00:00.000000000", strEndDate + " 23:59:59.000000000", strRequestedPostalCode);

    ReportViewModel reportViewModel = new ReportViewModel();

    reportViewModel.ReportDataByPostalCodeTable = rsReportDataByPostalCode;
    
    return View("_ExportSummaryToExcel", reportViewModel);
}

@using System.Data;
@using BHTS.Service;
@using Microsoft.AspNetCore.Hosting;
@using NPOI.HSSF.UserModel;
@using NPOI.SS.UserModel;
@using NPOI.Util;
@using System.IO;
@using Microsoft.AspNetCore.Http;
@using System.Web;
@using NPOI.XSSF.UserModel;
@inject IHostingEnvironment _hostingEnvironment
@inject IHttpContextAccessor HttpContextAccessor
@model BHTS.Service.ViewModels.ReportViewModel


@{
    //Set the content type header with the razor directive
    Context.Response.ContentType = "application/vnd.ms-excel";

    // Set the content disposition header
    Context.Response.Headers.Add("Content-Disposition", "attachment; filename=\"Summary.xls\"");    
}

@{
    string strExceptionMessage ;

    try{

        string strNewPostalCode = "";

        string strRequestedPostalCode = "";         
        string strStartDate = "";
        string strEndDate = "";

        //Get the postal code, start date and end date for the requested data.
        strRequestedPostalCode = ViewBag.RequestedPostalCode;
        strStartDate = ViewBag.StartDate;
        strEndDate = ViewBag.EndDate;

        //Get the Excel worksheet that is used as the template.
        
        String strExcelTemplatePath = ""; 
        strExcelTemplatePath = _hostingEnvironment.ContentRootPath + "\\Views\\Reports\\SummaryByAgeStagePostalBlank.xls";
        HSSFWorkbook wb = new HSSFWorkbook(new FileStream(strExcelTemplatePath, FileMode.Open, FileAccess.ReadWrite));  
        
        //Get the first sheet in the workbook.
        ISheet sheet = wb.GetSheetAt(0);

        DataTable rsReportDataByPostalCode;

        //Get the summary requested data.   
        rsReportDataByPostalCode = Model.ReportDataByPostalCodeTable;

        int rowCount = rsReportDataByPostalCode.Rows.Count;
        int currentRowNumber = 2;

        //Set the title at the top of the Excel sheet.
        sheet.GetRow(0).GetCell(0).SetCellValue("Summary Data For Postal Code " + strRequestedPostalCode );
        sheet.GetRow(0).GetCell(4).SetCellValue("Start Date: " + strStartDate );
        sheet.GetRow(0).GetCell(7).SetCellValue("End Date: " + strEndDate );

        //rsReportDataByPostalCode.beforeFirst();

        if(rsReportDataByPostalCode != null && rowCount!=0)
        {   
            try 
            {
                //Iterate through the resultset.
                foreach (DataRow rsReportDataByPostalCodeRow in @rsReportDataByPostalCode.Rows)
                {        
                    strNewPostalCode = rsReportDataByPostalCodeRow["Postal_Code"].ToString();

                    //Set the resultset values into the appropriate cells in the Excel spreadsheet.
                    sheet.GetRow(currentRowNumber).GetCell(0).SetCellValue(rsReportDataByPostalCodeRow["Stage"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(1).SetCellValue(rsReportDataByPostalCodeRow["<20"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(2).SetCellValue(rsReportDataByPostalCodeRow["20-24"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(3).SetCellValue(rsReportDataByPostalCodeRow["25-29"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(4).SetCellValue(rsReportDataByPostalCodeRow["30-34"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(5).SetCellValue(rsReportDataByPostalCodeRow["35-39"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(6).SetCellValue(rsReportDataByPostalCodeRow["40-44"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(7).SetCellValue(rsReportDataByPostalCodeRow["45-49"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(8).SetCellValue(rsReportDataByPostalCodeRow["50-54"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(9).SetCellValue(rsReportDataByPostalCodeRow["55-59"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(10).SetCellValue(rsReportDataByPostalCodeRow["60-64"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(11).SetCellValue(rsReportDataByPostalCodeRow["65-69"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(12).SetCellValue(rsReportDataByPostalCodeRow["70-74"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(13).SetCellValue(rsReportDataByPostalCodeRow["75-79"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(14).SetCellValue(rsReportDataByPostalCodeRow["80-84"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(15).SetCellValue(rsReportDataByPostalCodeRow["85-89"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(16).SetCellValue(rsReportDataByPostalCodeRow["90-94"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(17).SetCellValue(rsReportDataByPostalCodeRow["95-99"].ToString());
                    sheet.GetRow(currentRowNumber).GetCell(18).SetCellValue(rsReportDataByPostalCodeRow["100+"].ToString());

                    currentRowNumber++;

                } //end foreach      
            }
            catch (Exception ex)
            {
                strExceptionMessage = ex.Message;
            }      

        }//end if    

        var originalBody = Context.Response.Body;
    
        wb.Write(originalBody);
        HttpContextAccessor.HttpContext.Response.Body.Flush();
        HttpContextAccessor.HttpContext.Response.Body.Close();      
    }
    catch (Exception ex)
    { 
        
    } 
}