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Formatting dates and currency when exporting to Excel

I have some code that's creating a DataTable, and then converting it to an Excel spreadsheet. Code is below:
DataTable table = (DataTable)JsonConvert.DeserializeObject(JsonConvert.SerializeObject(exportDtos), typeof(DataTable));
using var stream = new MemoryStream();
using (SpreadsheetDocument document = SpreadsheetDocument.Create(stream, SpreadsheetDocumentType.Workbook))
{
WorkbookPart workbookPart = document.AddWorkbookPart();
workbookPart.Workbook = new Workbook();
WorksheetPart worksheetPart = workbookPart.AddNewPart<WorksheetPart>();
var sheetData = new SheetData();
worksheetPart.Worksheet = new Worksheet(sheetData);
Sheets sheets = workbookPart.Workbook.AppendChild(new Sheets());
Sheet sheet = new Sheet() { Id = workbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "Sheet1" };
sheets.Append(sheet);
Row headerRow = new Row();
List<String> columns = new List<string>();
foreach (DataColumn column in table.Columns)
{
columns.Add(column.ColumnName);
Cell cell = new Cell();
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(column.ColumnName);
headerRow.AppendChild(cell);
}
sheetData.AppendChild(headerRow);
foreach (DataRow dsrow in table.Rows)
{
Row newRow = new Row();
foreach (String col in columns)
{
Cell cell = new Cell();
var celltype = dsrow[col].GetType();
if (dsrow[col].GetType() == typeof(double))
{
cell.DataType = CellValues.Number;
cell.CellValue = new CellValue(decimal.Parse(dsrow[col].ToString()));
cell.StyleIndex = 2;
}
else if (dsrow[col].GetType() == typeof(DateTime))
{
cell.DataType = CellValues.Date;
cell.CellValue = new CellValue(DateTime.Parse(dsrow[col].ToString()).ToOADate());
cell.StyleIndex = 1;
}
else
{
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(dsrow[col].ToString());
}
newRow.AppendChild(cell);
}
sheetData.AppendChild(newRow);
}
workbookPart.Workbook.Save();
}
The problem is that dates and decimal values were stored as text, and not sorting correctly in Excel, so I added these two conditions:
if (dsrow[col].GetType() == typeof(double))
{
cell.DataType = CellValues.Number;
cell.CellValue = new CellValue(decimal.Parse(dsrow[col].ToString()));
cell.StyleIndex = 2;
}
else if (dsrow[col].GetType() == typeof(DateTime))
{
cell.DataType = CellValues.Date;
cell.CellValue = new CellValue(DateTime.Parse(dsrow[col].ToString()).ToOADate());
cell.StyleIndex = 1;
}
else
{
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(dsrow[col].ToString());
}
There's a few problems:
The StyleIndex doesn't work for the double values, it's not formatting the cell with 2 decimal places. It also gives this Repair error:
We found a problem with some content in 'file.xlsx' ... Excel was able to open the file by repairing or removing the unreadable content.
Excel completed file level validation and repair. Some parts of this workbook may have been repaired or discarded.
If I remove the StyleIndex, I don't get the error, but it still doesn't format the cell with 2 decimal places.
The date value is always a number value, not a date. And it always gives the repair error.
I've looked at several different forums saying to try different things, and I can't get any of them to work. I've changed the StyleIndex to different suggested numbers, changed the DataType, and it's always the same problems. Is there a consistent answer to how to format dates and currency values?

Why does my WorkbookView sequence keep returning "null" value with OpenXml?

I have created a download button in C#/asp.net, which takes a GridView, converts it to a data table, and then stores it into a .xlsx file. What I want to do after is be able to change the active tab of the spreadsheet I created.
Here is the code below:
protected void downloadBtn_Click(object sender, EventArgs e)
{
using (var spreadSheet = SpreadsheetDocument.Create(Server.MapPath("~/Downloads/TestSheet.xlsx"), DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook))
{
WorkbookPart workbookPart = spreadSheet.AddWorkbookPart();
workbookPart.Workbook = new Workbook();
WorksheetPart worksheetPart = workbookPart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet(new SheetData());
//Fine up to this point
spreadSheet.WorkbookPart.Workbook.Sheets = new Sheets();
DataTable table = new DataTable();
//Converts GridView into Data Table **
for (int i = 0; i < gvEmployee.HeaderRow.Cells.Count - 1; i++)
{
table.Columns.Add(gvEmployee.HeaderRow.Cells[i + 1].Text);
}
// fill rows
for (int i = 0; i < gvEmployee.Rows.Count; i++)
{
DataRow dr = table.NewRow();
for (int j = 0; j < gvEmployee.Columns.Count - 1; j++)
{
dr[j] = gvEmployee.Rows[i].Cells[j + 1].Text;
}
table.Rows.Add(dr);
}
var sheetPart = spreadSheet.WorkbookPart.AddNewPart<WorksheetPart>();
var sheetData = new SheetData();
sheetPart.Worksheet = new Worksheet(sheetData);
Sheets sheets = spreadSheet.WorkbookPart.Workbook.GetFirstChild<Sheets>();
string relationshipId = spreadSheet.WorkbookPart.GetIdOfPart(sheetPart);
uint sheetId = 1;
if (sheets.Elements<Sheet>().Count() > 0)
{
sheetId = sheets.Elements<Sheet>().Select(s => s.SheetId.Value).Max() + 1;
}
Sheet sheet = new Sheet() { Id = relationshipId, SheetId = sheetId, Name = "TestSheet" };
sheets.Append(sheet);
Row headerRow = new Row();
List<String> columns = new List<string>();
foreach (DataColumn column in table.Columns)
{
columns.Add(column.ColumnName);
Cell cell = new Cell();
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(column.ColumnName);
headerRow.AppendChild(cell);
}
sheetData.AppendChild(headerRow);
foreach (DataRow dsrow in table.Rows)
{
Row newRow = new Row();
foreach (String col in columns)
{
Cell cell = new Cell();
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(dsrow[col].ToString()); //
newRow.AppendChild(cell);
}
sheetData.AppendChild(newRow);
}
Sheet sheet2 = new Sheet() { Id = spreadSheet.WorkbookPart.GetIdOfPart(sheetPart), SheetId = 2, Name = "AdditionalSheet" };
sheets.Append(sheet2);
var sheetIndex = workbookPart.Workbook.Descendants<Sheet>().ToList().IndexOf(sheet2);
WorkbookView workbookView = workbookPart.Workbook.Descendants<WorkbookView>().FirstOrDefault(); //new WorkbookView();
workbookView.ActiveTab = Convert.ToUInt32(sheetIndex);
workbookPart.Workbook.Save();
spreadSheet.Close();
}
}
When I try to run this code, it throws an error on the "workbookView.ActiveTab" at the last few lines stating
System.NullReferenceException: 'Object reference not set to an instance of an object.'
workbookView was null.
Any ideas as to why its doing this?

Okay, I just figured out what was wrong, there was no WorkbookView initialized, as I thought it thought it didn't need to be. But you have to actually make a WorkbookView of your workbook before you can change it. I just needed this one line:
workbookPart.Workbook.Append(new BookViews(new WorkbookView()));

Open XML Sheetview Right to left

I need to add SheetView settings in ExporToExcel Class. But after export, it's showing that Excel Cell Content is empty even though the worksheet is created and SheetView settings are set. I checked all of the posts on this site and other site's as well, but I was not successful. Every time I am getting a Document corrupted message or the spreadsheet is empty.
private static void WriteExcelFile(DataSet ds, SpreadsheetDocument spreadsheet)
{
spreadsheet.AddWorkbookPart();
spreadsheet.WorkbookPart.Workbook = new DocumentFormat.OpenXml.Spreadsheet.Workbook();
spreadsheet.WorkbookPart.Workbook.Append(new BookViews(new WorkbookView()));
WorkbookStylesPart workbookStylesPart = spreadsheet.WorkbookPart.AddNewPart<WorkbookStylesPart>("rIdStyles");
//Stylesheet stylesheet = new Stylesheet();
workbookStylesPart.Stylesheet = CreateStylesheet();
uint worksheetNumber = 1;
Sheets sheets = spreadsheet.WorkbookPart.Workbook.AppendChild<Sheets>(new Sheets());
foreach (DataTable dt in ds.Tables)
{
string worksheetName = dt.TableName;
WorksheetPart newWorksheetPart = spreadsheet.WorkbookPart.AddNewPart<WorksheetPart>();
Sheet sheet = new Sheet() { Id = spreadsheet.WorkbookPart.GetIdOfPart(newWorksheetPart), SheetId = worksheetNumber, Name = worksheetName };
newWorksheetPart.Worksheet = new Worksheet(new SheetViews(new SheetView() { WorkbookViewId=0,RightToLeft=true}),new SheetData());
newWorksheetPart.Worksheet.Save();
sheets.Append(sheet);
WriteDataTableToExcelWorksheet(dt, newWorksheetPart);
worksheetNumber++;
}
spreadsheet.WorkbookPart.Workbook.Save();
}
private static void WriteDataTableToExcelWorksheet(DataTable dt, WorksheetPart worksheetPart)
{
OpenXmlWriter writer = OpenXmlWriter.Create(worksheetPart, Encoding.ASCII);
writer.WriteStartElement(new Worksheet());
writer.WriteStartElement(new SheetData());
string cellValue = "";
int numberOfColumns = dt.Columns.Count;
bool[] IsNumericColumn = new bool[numberOfColumns];
bool[] IsDateColumn = new bool[numberOfColumns];
string[] excelColumnNames = new string[numberOfColumns];
for (int n = 0; n < numberOfColumns; n++)
excelColumnNames[n] = GetExcelColumnName(n);
//
// Create the Header row in our Excel Worksheet
//
uint rowIndex = 1;
writer.WriteStartElement(new Row { RowIndex = rowIndex });
for (int colInx = 0; colInx < numberOfColumns; colInx++)
{
DataColumn col = dt.Columns[colInx];
AppendTextCell(excelColumnNames[colInx] + "1", col.ColumnName, ref writer);
IsNumericColumn[colInx] = (col.DataType.FullName == "System.Decimal") || (col.DataType.FullName == "System.Int32") || (col.DataType.FullName == "System.Double") || (col.DataType.FullName == "System.Single");
IsDateColumn[colInx] = (col.DataType.FullName == "System.DateTime");
}
writer.WriteEndElement(); // End of header "Row"
double cellNumericValue = 0;
foreach (DataRow dr in dt.Rows)
{
++rowIndex;
writer.WriteStartElement(new Row { RowIndex = rowIndex });
for (int colInx = 0; colInx < numberOfColumns; colInx++)
{
cellValue = dr.ItemArray[colInx].ToString();
cellValue = ReplaceHexadecimalSymbols(cellValue);
if (IsNumericColumn[colInx])
{
cellNumericValue = 0;
if (double.TryParse(cellValue, out cellNumericValue))
{
cellValue = cellNumericValue.ToString();
AppendNumericCell(excelColumnNames[colInx] + rowIndex.ToString(), cellValue, ref writer);
}
}
else if (IsDateColumn[colInx])
{
// This is a date value.
DateTime dtValue;
string strValue = "";
if (DateTime.TryParse(cellValue, out dtValue))
strValue = dtValue.ToShortDateString();
AppendTextCell(excelColumnNames[colInx] + rowIndex.ToString(), strValue, ref writer);
}
else
{
AppendTextCell(excelColumnNames[colInx] + rowIndex.ToString(), cellValue, ref writer);
}
}
writer.WriteEndElement(); // End of Row
}
writer.WriteEndElement(); // End of SheetData
writer.WriteEndElement(); // End of worksheet
writer.Close();
}

The code to make the sheet read RightToLeft sheet was correct. However, the code for WriteDataTableToExcelWorksheet and CreateStylesheet was not complete and had some problems.
I was able to find the original code for the WriteDataTableToExcelWorksheet at this link. Then I reversed engineered a plain Excel file with the Open XML Productivity Tool to C# code and reused a method to create a new Stylesheet.
The excel file I generated with this code is shown here:
I've pushed this new code to GitHub. There is a wrapper WPF application that guides where to generate the file on your machine.
Here is a guide on installing the Open XML Productivity Tool.

Open XML Export datatable to excel directly on disk

I want to export datatable to xlsx directly to my disk instead of giving destination path and saving file on server.
I have following function :
private void ExportToCSVFileOpenXML(DataTable dt, string destination)
{
DataSet ds = new DataSet();
DataTable dtCopy = new DataTable();
dtCopy = dt.Copy();
ds.Tables.Add(dtCopy);
try
{
var workbook = SpreadsheetDocument.Create(Server.MapPath("~/" + destination.Replace("/","").Replace(":","")), DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook);
{
var workbookPart = workbook.AddWorkbookPart();
workbook.WorkbookPart.Workbook = new DocumentFormat.OpenXml.Spreadsheet.Workbook();
workbook.WorkbookPart.Workbook.Sheets = new DocumentFormat.OpenXml.Spreadsheet.Sheets();
foreach (System.Data.DataTable table in ds.Tables)
{
var sheetPart = workbook.WorkbookPart.AddNewPart<WorksheetPart>();
var sheetData = new DocumentFormat.OpenXml.Spreadsheet.SheetData();
sheetPart.Worksheet = new DocumentFormat.OpenXml.Spreadsheet.Worksheet(sheetData);
DocumentFormat.OpenXml.Spreadsheet.Sheets sheets = workbook.WorkbookPart.Workbook.GetFirstChild<DocumentFormat.OpenXml.Spreadsheet.Sheets>();
string relationshipId = workbook.WorkbookPart.GetIdOfPart(sheetPart);
uint sheetId = 1;
if (sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Count() > 0)
{
sheetId =
sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Select(s => s.SheetId.Value).Max() + 1;
}
DocumentFormat.OpenXml.Spreadsheet.Sheet sheet = new DocumentFormat.OpenXml.Spreadsheet.Sheet() { Id = relationshipId, SheetId = sheetId, Name = table.TableName };
sheets.Append(sheet);
DocumentFormat.OpenXml.Spreadsheet.Row headerRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
List<String> columns = new List<string>();
foreach (System.Data.DataColumn column in table.Columns)
{
columns.Add(column.ColumnName);
DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(column.ColumnName);
headerRow.AppendChild(cell);
}
sheetData.AppendChild(headerRow);
foreach (System.Data.DataRow dsrow in table.Rows)
{
DocumentFormat.OpenXml.Spreadsheet.Row newRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
foreach (String col in columns)
{
DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(dsrow[col].ToString()); //
newRow.AppendChild(cell);
}
sheetData.AppendChild(newRow);
}
}
}
}
catch (Exception)
{
throw;
}
}
How can I directly export this to disk instead of saving on server by giving destination path as :
var workbook = SpreadsheetDocument.Create(Server.MapPath("~/" + destination.Replace("/","").Replace(":","")), DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook);
Please help me.

SpreadsheetDocument.Create accepts a stream, string, or package as its first argument so we can just use a MemoryStream to create the workbook in memory and return a byte array.
It should be something like this:
public byte[] ExportToCSVFileOpenXML(DataTable dt)
{
byte[] returnBytes = null;
using (MemoryStream mem = new MemoryStream())
{
var workbook = SpreadsheetDocument.Create(mem, DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook);
// your code
workbook.WorkbookPart.Workbook.Save();
workbook.Close();
returnBytes = mem.ToArray();
}
return returnBytes;
}
Once you have a byte array passing it as a file should be quite easy.
If you are using MVC it should be something like this in your controler:
return File(ExportToCSVFileOpenXML(aTable), "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", "export.xlsx");

Alex answer lead me to correct answer.
I did following thing :
private byte[] ExportToCSVFileOpenXML(DataTable dt)
{
DataSet ds = new DataSet();
DataTable dtCopy = new DataTable();
dtCopy = dt.Copy();
ds.Tables.Add(dtCopy);
try
{
byte[] returnBytes = null;
MemoryStream mem = new MemoryStream();
var workbook = SpreadsheetDocument.Create(mem, DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook);
{
var workbookPart = workbook.AddWorkbookPart();
workbook.WorkbookPart.Workbook = new DocumentFormat.OpenXml.Spreadsheet.Workbook();
workbook.WorkbookPart.Workbook.Sheets = new DocumentFormat.OpenXml.Spreadsheet.Sheets();
foreach (System.Data.DataTable table in ds.Tables)
{
var sheetPart = workbook.WorkbookPart.AddNewPart<WorksheetPart>();
var sheetData = new DocumentFormat.OpenXml.Spreadsheet.SheetData();
sheetPart.Worksheet = new DocumentFormat.OpenXml.Spreadsheet.Worksheet(sheetData);
DocumentFormat.OpenXml.Spreadsheet.Sheets sheets = workbook.WorkbookPart.Workbook.GetFirstChild<DocumentFormat.OpenXml.Spreadsheet.Sheets>();
string relationshipId = workbook.WorkbookPart.GetIdOfPart(sheetPart);
uint sheetId = 1;
if (sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Count() > 0)
{
sheetId =
sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Select(s => s.SheetId.Value).Max() + 1;
}
DocumentFormat.OpenXml.Spreadsheet.Sheet sheet = new DocumentFormat.OpenXml.Spreadsheet.Sheet() { Id = relationshipId, SheetId = sheetId, Name = table.TableName };
sheets.Append(sheet);
DocumentFormat.OpenXml.Spreadsheet.Row headerRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
List<String> columns = new List<string>();
foreach (System.Data.DataColumn column in table.Columns)
{
columns.Add(column.ColumnName);
DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(column.ColumnName);
headerRow.AppendChild(cell);
}
sheetData.AppendChild(headerRow);
foreach (System.Data.DataRow dsrow in table.Rows)
{
DocumentFormat.OpenXml.Spreadsheet.Row newRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
foreach (String col in columns)
{
DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(dsrow[col].ToString()); //
newRow.AppendChild(cell);
}
sheetData.AppendChild(newRow);
}
}
}
workbook.WorkbookPart.Workbook.Save();
workbook.Close();
returnBytes = mem.ToArray();
return returnBytes;
}
catch (Exception)
{
throw;
}
}
Called this function as:
protected void hlInCorrectRecords_Click(object sender, EventArgs e)
{
lblmsg.Text = "";
DataSet dsDtUploadedSummary = (DataSet)ViewState["dsDtUploadedSummary"];
if (dsDtUploadedSummary.Tables.Count > 0)
{
DataTable dtFreshRecords = dsDtUploadedSummary.Tables[4];
if (dtFreshRecords.Rows.Count > 0 && dtFreshRecords != null)
{
Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
string filename = #"IncorrectRecordsUploaded_" + DateTime.Now.ToString();
Response.AddHeader("Content-Disposition", "inline;filename=" + filename.Replace("/", "").Replace(":", "")+".xlsx");
Response.BinaryWrite(ExportToCSVFileOpenXML(dtFreshRecords));
Response.Flush();
Response.End();
}
else
{
lblmsg.Text = "No Data To Export";
}
}
else
{
lblmsg.Text = "No Data To Export";
}
}
Thanks Alex. I am using plain ASP.NET not MVC

Export Sql data to Excel very slow

I am exporting Sql data to Excel. The code I am using currently is :
DataTable dt = new DataTable();
// Create sql connection string
string conString = "Data Source=DELL\\SQLSERVER1;Trusted_Connection=True;DATABASE=Zelen;CONNECTION RESET=FALSE";
SqlConnection sqlCon = new SqlConnection(conString);
sqlCon.Open();
SqlDataAdapter da = new SqlDataAdapter("select LocalSKU,ItemName, QOH,Price,Discontinued,CAST(Barcode As varchar(25)) As Barcode,Integer2,Integer3,ISNULL(SalePrice,0.0000)AS SalePrice,SaleOn,ISNULL(Price2,0.0000)AS Price2 from dbo.Inventory", sqlCon);
System.Data.DataTable dtMainSQLData = new System.Data.DataTable();
da.Fill(dtMainSQLData);
DataColumnCollection dcCollection = dtMainSQLData.Columns;
// Export Data into EXCEL Sheet
Microsoft.Office.Interop.Excel.ApplicationClass ExcelApp = new Microsoft.Office.Interop.Excel.ApplicationClass();
ExcelApp.Application.Workbooks.Add(Type.Missing);
int i = 1;
int j = 1;
int s = 1;
//header row
foreach (DataColumn col in dtMainSQLData.Columns)
{
ExcelApp.Cells[i, j] = col.ColumnName;
j++;
ExcelApp.Rows.AutoFit();
ExcelApp.Columns.AutoFit();
}
i++;
//data rows
foreach (DataRow row in dtMainSQLData.Rows)
{
for (int k = 1; k < dtMainSQLData.Columns.Count + 1; k++)
{
ExcelApp.Cells[i, k] = "'" + row[k - 1].ToString();
}
i++;
s++;
Console.Write(s);
Console.Write("\n\r");
ExcelApp.Columns.AutoFit();
ExcelApp.Rows.AutoFit();
}
var b = Environment.CurrentDirectory + #"\Sheet1.xlsx";
ExcelApp.ActiveWorkbook.SaveCopyAs(b);
ExcelApp.ActiveWorkbook.Saved = true;
ExcelApp.Quit();
Console.WriteLine(".xlsx file Exported succssessfully.");
Takes are 70000 rows in my sql database. I am running this script in Console application.
It takes more then an hour to export it to excel file.
How can I use this to export it faster?
Examples would be appreciated.

Option 1:
See this answer. Use a library called ClosedXML to write the data to Excel.
Option 2:
Get a range big enough for all of the data and set the value equal to a 2 dimensional range. This works very fast without another referencing another library. I tried with 70000 records.
// Get an excel instance
Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();
// Get a workbook
Workbook wb = excel.Workbooks.Add();
// Get a worksheet
Worksheet ws = wb.Worksheets.Add();
ws.Name = "Test Export";
// Add column names to the first row
int col = 1;
foreach (DataColumn c in table.Columns) {
ws.Cells[1, col] = c.ColumnName;
col++;
}
// Create a 2D array with the data from the table
int i = 0;
string[,] data = new string[table.Rows.Count, table.Columns.Count];
foreach (DataRow row in table.Rows) {
int j = 0;
foreach (DataColumn c in table.Columns) {
data[i,j] = row[c].ToString();
j++;
}
i++;
}
// Set the range value to the 2D array
ws.Range[ws.Cells[2, 1], ws.Cells[table.Rows.Count + 1, table.Columns.Count]].value = data;
// Auto fit columns and rows, show excel, save.. etc
excel.Columns.AutoFit();
excel.Rows.AutoFit();
excel.Visible = true;
Edit: This version exported a million records on my machine it takes about a minute. This example uses Excel interop and breaks the rows in to chunks of 100,000.
// Start a stopwatch to time the process
System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
sw.Start();
// Check if there are rows to process
if (table != null && table.Rows.Count > 0) {
// Determine the number of chunks
int chunkSize = 100000;
double chunkCountD = (double)table.Rows.Count / (double)chunkSize;
int chunkCount = table.Rows.Count / chunkSize;
chunkCount = chunkCountD > chunkCount ? chunkCount + 1 : chunkCount;
// Instantiate excel
Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();
// Get a workbook
Workbook wb = excel.Workbooks.Add();
// Get a worksheet
Worksheet ws = wb.Worksheets.Add();
ws.Name = "Test Export";
// Add column names to excel
int col = 1;
foreach (DataColumn c in table.Columns) {
ws.Cells[1, col] = c.ColumnName;
col++;
}
// Build 2D array
int i = 0;
string[,] data = new string[table.Rows.Count, table.Columns.Count];
foreach (DataRow row in table.Rows) {
int j = 0;
foreach (DataColumn c in table.Columns) {
data[i, j] = row[c].ToString();
j++;
}
i++;
}
int processed = 0;
int data2DLength = data.GetLength(1);
for (int chunk = 1; chunk <= chunkCount; chunk++) {
if (table.Rows.Count - processed < chunkSize) chunkSize = table.Rows.Count - processed;
string[,] chunkData = new string[chunkSize, data2DLength];
int l = 0;
for (int k = processed; k < chunkSize + processed; k++) {
for (int m = 0; m < data2DLength; m++) {
chunkData[l,m] = table.Rows[k][m].ToString();
}
l++;
}
// Set the range value to the chunk 2d array
ws.Range[ws.Cells[2 + processed, 1], ws.Cells[processed + chunkSize + 1, data2DLength]].value = chunkData;
processed += chunkSize;
}
// Auto fit columns and rows, show excel, save.. etc
excel.Columns.AutoFit();
excel.Rows.AutoFit();
excel.Visible = true;
}
// Stop the stopwatch and display the seconds elapsed
sw.Stop();
MessageBox.Show(sw.Elapsed.TotalSeconds.ToString());

If you save your data to as CSV formant you can load that into Excel, Here is some code i have modified from The Code Project site here http://www.codeproject.com/Tips/665519/Writing-a-DataTable-to-a-CSV-file
public class Program
{
static void Main(string[] args)
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
DataTable dt = new DataTable();
// Create Connection object
using (SqlConnection conn = new SqlConnection(#"<Your Connection String>"))
{
// Create Command object
conn.Open();
using (SqlCommand cmd = new SqlCommand("SELECT * FROM <Your Table>", conn))
{
using (SqlDataReader reader = cmd.ExecuteReader())
{
try
{
dt.Load(reader);
using (StreamWriter writer = new StreamWriter("C:\\Temp\\dump.csv"))
{
DataConvert.ToCSV(dt, writer, false);
}
}
catch (Exception)
{
throw;
}
}
}
}
// Stop timing
stopwatch.Stop();
// Write result
Console.WriteLine("Time elapsed: {0}",
stopwatch.Elapsed);
Console.ReadKey();
}
}
public static class DataConvert
{
public static void ToCSV(DataTable sourceTable, TextWriter writer, bool includeHeaders)
{
if (includeHeaders)
{
List<string> headerValues = new List<string>();
foreach (DataColumn column in sourceTable.Columns)
{
headerValues.Add(QuoteValue(column.ColumnName));
}
writer.WriteLine(String.Join(",", headerValues.ToArray()));
}
string[] items = null;
foreach (DataRow row in sourceTable.Rows)
{
items = row.ItemArray.Select(o => QuoteValue(o.ToString())).ToArray();
writer.WriteLine(String.Join(",", items));
}
writer.Flush();
}
private static string QuoteValue(string value)
{
return String.Concat("\"", value.Replace("\"", "\"\""), "\"");
}
}
}
On my PC this took 30 seconds to process 1 million records...

you can try this function:
After set your data in a datatable.
Public Shared Sub ExportDataSetToExcel(ByVal ds As DataTable, ByVal filename As String)
Dim response As HttpResponse = HttpContext.Current.Response
response.Clear()
response.Buffer = True
response.Charset = ""
response.ContentType = "application/vnd.ms-excel"
Using sw As New StringWriter()
Using htw As New HtmlTextWriter(sw)
Dim dg As New DataGrid()
dg.DataSource = ds
dg.DataBind()
dg.RenderControl(htw)
response.Charset = "UTF-8"
response.ContentEncoding = System.Text.Encoding.UTF8
response.BinaryWrite(System.Text.Encoding.UTF8.GetPreamble())
response.Output.Write(sw.ToString())
response.[End]()
End Using
End Using
End Sub

I prefer Microsoft Open XML SDK's Open XML Writer. Open XML is the format all the new office files are in.
Export a large data query (60k+ rows) to Excel
Vincent Tan has a nice article on the topic.
http://polymathprogrammer.com/2012/08/06/how-to-properly-use-openxmlwriter-to-write-large-excel-files/