I think most things can be done via NPOI, I usually use the POI Java Docs when I’m looking for something because I find them easier to search/navigate.

http://poi.apache.org/apidocs/overview-summary.html

I’ve also ported over a few bug fixes to NPOI, but in general Tony, the NPOI project creator is getting the bug fixes applied really quick and is always watching the forum/bug reports. If you find something broken, posting in the discussion/bug thread on NPOI CodePlex page is a good place to report it. You can also look at POI forums, cause you might see it was also found and fixed there. I was on my own custom build of NPOI for awhile, but as of 1.2.3 I’m back on the official build. I don’t think I have any changes in my current production built, but I tweak things so often it’s hard to remember what I did in weeks prior.

Another issue worth noting: while filing the excel template using NPOI’s “Get…” syntax, an issue arose where the cell format in the XLS template, which started out as “General”, was not being treated as a number after data-fill. The cells with integers were generating Excel’s little cell formatting “green triangle” warning. And the charts relying on those integers were then failing to display. As a result, I tweaked the CASE statement for System.Int to convert back to Int, as opposed to string.
After that, no more cell warning messages appeared, and the charts loaded.

        Public Shared Sub ExcelUpdateRow(ByVal _myDataTable As DataTable, ByVal _sheet As HSSFSheet)

            Dim rowIndex As Integer = 1

            For Each row As DataRow In _myDataTable.Rows

                Dim dataRow As HSSFRow = CType(_sheet.GetRow(rowIndex), HSSFRow)
                For Each column As DataColumn In _myDataTable.Columns

                    ' dataRow.GetCell(column.Ordinal).SetCellValue(row(column).ToString())

                    Select Case column.DataType.FullName
                        Case "System.String"
                            dataRow.GetCell(column.Ordinal).SetCellValue(row(column).ToString())
                            Exit Select
                        Case "System.Double", "System.Decimal"
                            dataRow.GetCell(column.Ordinal).SetCellValue([Double].Parse(row(column).ToString()))
                            [Double].Parse(row(column).ToString())
                            Exit Select
                        Case "System.Int", "System.Int32", "System.Int64"
                            dataRow.GetCell(column.Ordinal).SetCellValue(CInt(row(column).ToString()))
                            Exit Select
                        Case Else
                            dataRow.GetCell(column.Ordinal).SetCellValue(row(column).ToString())
                            Exit Select
                    End Select
                Next
                rowIndex += 1
            Next

        End Sub

As for why your DataTable results aren’t matching… I’m not sure without a little more information, but here is what I normally do when I pull the data and want to use it multiple times.

This example is simplified, normally I would pass criteria to the GetData() and use the criteria in the “cacheKey” variable.

        private DataTable GetData()
        {
            DataTable dt;

            string cacheKey = "Key Based on Criteria";

            if (Cache[cacheKey] != null)
            {
                dt = (DataTable)Cache[cacheKey];
            }
            else
            {
                // Get Your DataTable Here
                Cache.Add(cacheKey, dt, null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration,
                          CacheItemPriority.Low, null);
            }

            return dt;
        }

    // Here is how I call this method and use the DataTable that came from DB or Cache if it has previously been queried.
    DataTable dt = GetData();

Hope this helps, let me know if you have questions.

For instance, if you have a web page, and then a report version of that same web page, do you re-query the database and open a new page, or do you work with a copy of the DataTable that’s part of the web page?

Independent of NPOI, I’m running into an issue where the DataTable from the Page_Load event pulls all the correct data, but a DataTable from a DataTable variable in code behind isn’t putting out the data correctly. (Sorry for yet another question… )