Slow loop over data table collection - for-loop

Question

I am updating values in an Excel workbook using values from a MySQL database. There are just eleven rows in the WorkbookMap list, and six DataTables in the RptValueSet DataSet. I've proven that the problem is in this loop, not in the communication with the database. Getting the results is fast, but writing them to the workbook is slow. The code below works fine when the DataTables in the DataSet are small - such as a 3-column, 7-row results set, and I receive the updated Excel workbook almost instantly. However, the loop slows down noticeably when the results set increases; a 3-column, 50-row DataTable results in a 7 - 10 second delay in returning the updated Excel workbook. I'm not sure I really need to put the DataTables into a collection, but that's the only way I could figure out how to iterate over them. Any tips on optimizing this loop would be much appreciated!
// Create a list to contain the destination for the data in the workbook
List<WorkbookMap> wbMap = new List<WorkbookMap>();
// Create a new data set to contain results from database
DataSet RptValuesSet = new DataSet();
// RptValuesSet populated from database here....
// Create a collection so we can loop thru the dataset
DataTableCollection RptValuesColl = RptValuesSet.Tables;
for (int i = 0; i < RptValuesColl.Count; i++)
{
DataTable tbl = RptValuesColl[i];
// Find the correct entry in the workbook map
for (int j = 0; j < wbMap.Count; j++)
{
if (wbMap[j].SPCall == tbl.TableName)
{
// Write the results to the correct location in the workbook
MovingColumnRef = wbMap[j].StartColumn;
for (int c = 1; c < tbl.Columns.Count; c++)
{
row = wbMap[j].StartRow; // start at the top row for each new column
for (int r = 0; r < tbl.Rows.Count; r++)
{
// Write the database value to the workbook given the sheetName and cell address
UpdateValue(wbMap[j].SheetName, MovingColumnRef + row, tbl.Rows[r][c].ToString(), 0, wbMap[j].String);
row++;
}
MovingColumnRef = IncrementColRef(MovingColumnRef);
}
}
}
}

Answer 1

Without delving deeply into your code. I noticed you said that you believe the slowness is coming from writing to the sheet. Try putting the data into an Array first before updating the workbook. E.g. you would write to the sheet like this. anchorRangeName is the name of a range which would be only one cell in the workbook.
private void WriteResultToRange(Excel.Workbook wb, string anchorRangeName, object[,] resultArray)
{
Excel.Range resultRange = GetRange(anchorRangeName, wb).get_Resize(resultArray.GetLength(0), resultArray.GetLength(1));
resultRange.Value2 = resultArray;
}
You'll still need to get the data from the database into an array.