Exporting data to CSV from Controller

问题

I'm using the CsvHelper library in an ASP.NET MVC project to export data to CSV, and am finding that the exported data is either cut off, or in the case of smaller lists, no data is being written at all, and I'm receiving a blank CSV file.

My base controller has a method like this (which is called by controllers inheriting from this class to export lists of entities):

protected FileContentResult GetExportFileContentResult(IList data, string filename)
    {
        using (var memoryStream = new MemoryStream())
        {
            using (var streamWriter = new StreamWriter(memoryStream))
            {
                using (var csvWriter = new CsvWriter(streamWriter))
                {
                    csvWriter.WriteRecords(data);
                    return File(memoryStream.ToArray(), "text/csv", filename);
                }
            }
        }
    }

With exports of lists 1k+ items, it seems like the last few items get cut off. When the list of items is less than ~100, the CSV file returned is blank and contains no data.

I've tried writing straight to the output stream instead of a MemoryStream, and received the same results.

Also tried removing the using statements in case the stream was being disposed too early, but didn't result in any change either.

What is the correct way to use this library to create CSV files properly (ie. contains all rows, and works regardless of size of list)?

Edit

Decided to scrap using CsvHelper and went with a different library called CsvTools instead. This works without any problems. My code is below for reference.

protected FileContentResult GetExportFileContentResult(IList data, string filename)
{
    using (var memoryStream = new MemoryStream())
    {
            using (var streamWriter = new StreamWriter(memoryStream))
            {
                var dt = DataTable.New.FromEnumerable(data);
                dt.SaveToStream(streamWriter);
                return File(memoryStream.ToArray(), "text/csv", filename);
        }
    }
}

On a side note, tried Simon's suggestion below of using the memory stream directly instead of calling ToArray but got an error about the stream being closed, and haven't got round to debugging this yet.

回答1:

The reason is because you're not flushing the data in the writer to the stream. The writer will periodically flush itself when it's full, but you need to make sure to do it at the end.

Option 1:

using (var memoryStream = new MemoryStream())
using (var streamWriter = new StreamWriter(memoryStream))
using (var csvWriter = new CsvWriter(streamWriter))
{
    csvWriter.WriteRecords(data);
    streamWriter.Flush();
    memoryStream.Position = 0;
    return File(memoryStream, "text/csv", filename);
}

Option 2:

using (var memoryStream = new MemoryStream())
{
    using (var streamWriter = new StreamWriter(memoryStream))
    using (var csvWriter = new CsvWriter(streamWriter))
    {
        csvWriter.WriteRecords(data);
    } // The stream gets flushed here.
    memoryStream.Position = 0;
    return File(memoryStream, "text/csv", filename);
}

来源：https://stackoverflow.com/questions/21898462/exporting-data-to-csv-from-controller

标签

asp.net-mvc

csvhelper

csvtools