c# datatable to csv

Question

Could somebody please tell me why the following code is not working. The data is saved into the csv file, however the data is not separated. It all exists within the first cell of each row.

StringBuilder sb = new StringBuilder();

foreach (DataColumn col in dt.Columns)
{
    sb.Append(col.ColumnName + ',');
}

sb.Remove(sb.Length - 1, 1);
sb.Append(Environment.NewLine);

foreach (DataRow row in dt.Rows)
{
    for (int i = 0; i < dt.Columns.Count; i++)
    {
        sb.Append(row[i].ToString() + ",");
    }

    sb.Append(Environment.NewLine);
}

File.WriteAllText("test.csv", sb.ToString());

Thanks.

Answer 1

Here is an enhancement to vc-74's post that handles commas the same way Excel does. Excel puts quotes around data if the data has a comma but doesn't quote if the data doesn't have a comma.

    public static string ToCsv(this DataTable inDataTable, bool inIncludeHeaders = true)
    {
        var builder = new StringBuilder();
        var columnNames = inDataTable.Columns.Cast<DataColumn>().Select(column => column.ColumnName);
        if (inIncludeHeaders)
            builder.AppendLine(string.Join(",", columnNames));
        foreach (DataRow row in inDataTable.Rows)
        {
            var fields = row.ItemArray.Select(field => field.ToString().WrapInQuotesIfContains(","));
            builder.AppendLine(string.Join(",", fields));
        }

        return builder.ToString();
    }

    public static string WrapInQuotesIfContains(this string inString, string inSearchString)
    {
        if (inString.Contains(inSearchString))
            return "\"" + inString+ "\"";
        return inString;
    }

Answer 2

If your calling code is referencing the System.Windows.Forms assembly, you may consider a radically different approach. My strategy is to use the functions already provided by the framework to accomplish this in very few lines of code and without having to loop through columns and rows. What the code below does is programmatically create a DataGridView on the fly and set the DataGridView.DataSource to the DataTable. Next, I programmatically select all the cells (including the header) in the DataGridView and call DataGridView.GetClipboardContent(), placing the results into the Windows Clipboard. Then, I 'paste' the contents of the clipboard into a call to File.WriteAllText(), making sure to specify the formatting of the 'paste' as TextDataFormat.CommaSeparatedValue.

Here is the code:

public static void DataTableToCSV(DataTable Table, string Filename)
{
    using(DataGridView dataGrid = new DataGridView())
    {
        // Save the current state of the clipboard so we can restore it after we are done
        IDataObject objectSave = Clipboard.GetDataObject();

        // Set the DataSource
        dataGrid.DataSource = Table;
        // Choose whether to write header. Use EnableWithoutHeaderText instead to omit header.
        dataGrid.ClipboardCopyMode = DataGridViewClipboardCopyMode.EnableAlwaysIncludeHeaderText;
        // Select all the cells
        dataGrid.SelectAll();
        // Copy (set clipboard)
        Clipboard.SetDataObject(dataGrid.GetClipboardContent());
        // Paste (get the clipboard and serialize it to a file)
        File.WriteAllText(Filename,Clipboard.GetText(TextDataFormat.CommaSeparatedValue));              

        // Restore the current state of the clipboard so the effect is seamless
        if(objectSave != null) // If we try to set the Clipboard to an object that is null, it will throw...
        {
            Clipboard.SetDataObject(objectSave);
        }
    }
}

Notice I also make sure to preserve the contents of the clipboard before I begin, and restore it once I'm done, so the user does not get a bunch of unexpected garbage next time the user tries to paste. The main caveats to this approach is 1) Your class has to reference System.Windows.Forms, which may not be the case in a data abstraction layer, 2) Your assembly will have to be targeted for .NET 4.5 framework, as DataGridView does not exist in 4.0, and 3) The method will fail if the clipboard is being used by another process.

Anyways, this approach may not be right for your situation, but it is interesting none the less, and can be another tool in your toolbox.