ExportExcelWithoutTemplateDapper.cs

using ClosedXML.Excel;
using Dapper; 

private void ExportByBankWithoutMapping(long batchId,
                                                TemplateType templateType,
                                                string sprocName,
                                                string templatePath,
                                                string fileNameTemplate,
                                                string worksheetName = "Data")
        {
            var values = ExecuteQueryDapper(ConnectionString,
                sprocName,
                new { batchId });

            var fileName = GetFileNameWithTicks(fileNameTemplate);

            var excelContent = GenerateExcel(values, templatePath, worksheetName);
            _blobService.UploadContentBlobAsync(excelContent,
                fileName,
                templateType);
        }

        private string GetFileNameWithTicks(string originalFileName) =>
            string.Format(CultureInfo.InvariantCulture,
                          originalFileName,
                          DateTime.Now.Ticks);

        public string GenerateExcel(List<object[]> values,
                                    string templatePath,
                                    string worksheetName,
                                    int startRowPosition = 2,
                                    int startColumnPosition = 1)
        {
            try
            {
                using var memoryStream = new MemoryStream();
                using var workbook = new XLWorkbook(templatePath);

                var ws = workbook.Worksheet(worksheetName);

                var range = ws.Cell(startRowPosition, startColumnPosition).InsertData(values);

                workbook.SaveAs(memoryStream, new SaveOptions()
                {
                    ValidatePackage = true,
                    EvaluateFormulasBeforeSaving = true,
                    ConsolidateDataValidationRanges = true,
                    GenerateCalculationChain = true
                });

                var excelContentString = Convert.ToBase64String(memoryStream.ToArray());
                return excelContentString;
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
                throw;
            }
        }

        public List<object[]> ExecuteQueryDapper(string connectionString,
            string query,
            object parameters,
            CommandType commandType = CommandType.StoredProcedure)
        {
            using var connection = new SqlConnection(connectionString);
            var sprocResults = connection.Query(query, parameters, commandType: commandType).ToList(); //return IEnumerable of DapperRow
            var dictionaryOfResults = sprocResults.Select(x => (IDictionary<string, object>)x); //convert DapperRow into Dictionary<string, object>
            var resultList = dictionaryOfResults.Select(d => d.Values.ToArray()).ToList(); //Convert Dictionary into List<Object[]>
            return resultList;
        }