How to speed up dumping a DataTable into an Excel worksheet?

Question

I have the following routine that dumps a DataTable into an Excel worksheet.

    private void RenderDataTableOnXlSheet(DataTable dt, Excel.Worksheet xlWk,          


        

Answer 1

Interop has the fastest method called CopyFromRecordset but ADODB library has to be used

Definitely the fastest way/method and I have tried a few. Perhaps, not easy to use but the speed is astonishing:

https://docs.microsoft.com/en-us/office/vba/api/excel.range.copyfromrecordset

a short sample:

using ADODB;
using Microsoft.Office.Interop;

//--- datatable --- already exists
DataTable dt_data = new DataTable();
//--- or your dt code is here ..........


//--- mine has 3 columns ------

//--- code to populate ADO rs with DataTable data --- nothing special
//--- create empty rs .....
ADODB.Recordset rs = new ADODB.Recordset();
rs.CursorType = CursorTypeEnum.adOpenKeyset;
rs.CursorLocation = CursorLocationEnum.adUseClient;
rs.LockType = LockTypeEnum.adLockOptimistic;
rs.Fields.Append("employee_id",DataTypeEnum.adBSTR,255,FieldAttributeEnum.adFldIsNullable);
rs.Fields.Append("full_name", DataTypeEnum.adBSTR, 255, FieldAttributeEnum.adFldIsNullable);
rs.Fields.Append("start_date", DataTypeEnum.adBSTR, 10, FieldAttributeEnum.adFldIsNullable);
rs.Open();

//--- populate ADO rs with DataTable data ----    
for (int i = 0; i < dt_data.Rows.Count; i++)
{
    rs.AddNew();
    rs.Fields["employee_id"].Value = dt_data.Rows[i]["employee_id"].ToString();
    rs.Fields["full_name"].Value = dt_data.Rows[i]["full_name"].ToString();
    //--- if date is empty......
    if (dt_data.Rows[i]["start_date"].ToString().Length > 0)
    {
        rs.Fields["start_date"].Value = dt_data.Rows[i]["start_date"].ToString();
    }
    rs.Update();
}

Microsoft.Office.Interop.Excel.Application xlexcel;
Microsoft.Office.Interop.Excel.Workbook xlWorkBook;
Microsoft.Office.Interop.Excel.Worksheet xlWorkSheet;
object misValue = System.Reflection.Missing.Value;
xlexcel = new Microsoft.Office.Interop.Excel.Application();
xlexcel.Visible = true;


xlWorkBook = xlexcel.Workbooks.Add(misValue);
xlWorkSheet = (Microsoft.Office.Interop.Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);

//--- populate columns from rs --
for (int i = 0; i < rs.Fields.Count; i++)
{
    xlWorkSheet.Cells[1, i + 1] = rs.Fields[i].Name.ToString();
};

//----- .CopyFromRecordset method -- (rs object, MaxRows, MaxColumns) --- in this case 3 columns but it can 1,2,3 etc ------
xlWorkSheet.Cells[2, 1].CopyFromRecordset(CloneFilteredRecordset(rs), rs.RecordCount, 3);