Writing a DataTable to a CSV File

// C# Code

using System.Data;
using System.IO;
using System.Linq;

public static class Rfc4180Writer 
{
    public static void WriteDataTable(DataTable sourceTable, TextWriter writer, bool includeHeaders) 
    {
        if (includeHeaders) {
            IEnumerable<String> headerValues = sourceTable.Columns
                .OfType<DataColumn>()
                .Select(column => QuoteValue(column.ColumnName));
                
            writer.WriteLine(String.Join(",", headerValues));
        }

        IEnumerable<String> items = null;

        foreach (DataRow row in sourceTable.Rows) {
            items = row.ItemArray.Select(o => QuoteValue(o?.ToString() ?? String.Empty));
            writer.WriteLine(String.Join(",", items));
        }

        writer.Flush();
    }

    private static string QuoteValue(string value) 
    {
        return String.Concat("\"", 
        value.Replace("\"", "\"\""), "\"");
    }
} 

'VB Code

Imports System.Data
Imports System.IO
Imports System.Linq

Public Class Rfc4180Writer
    Public Shared Sub WriteDataTable(ByVal sourceTable As DataTable, _
    	ByVal writer As TextWriter, ByVal includeHeaders As Boolean)
        If (includeHeaders) Then
            Dim headerValues As IEnumerable(Of String) = sourceTable.Columns
                .OfType(Of DataColumn)
                .Select(Function(column) QuoteValue(column.ColumnName))

            writer.WriteLine(String.Join(",", headerValues))
        End If

        Dim items As IEnumerbale(Of String) = Nothing
        For Each row As DataRow In sourceTable.Rows
            items = row.ItemArray.Select(Function(obj) QuoteValue(If(obj?.ToString(), String.Empty)))
            writer.WriteLine(String.Join(",", items)
        Next

        writer.Flush()
    End Sub

    Private Shared Function QuoteValue(ByVal value As String) As String
        Return String.Concat("""", value.Replace("""", """"""), """")
    End Function
End Class 

// C# Code
public static class Program {
    public static void Main() {
        DataTable sourceTable = new DataTable();

        sourceTable.Columns.AddRange(new DataColumn[] {
            new DataColumn("ID", typeof(Guid)),
            new DataColumn("Date", typeof(DateTime)),
            new DataColumn("StringValue", typeof(string)),
            new DataColumn("NumberValue", typeof(int)),
            new DataColumn("BooleanValue", typeof(bool))
        });

        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String1", 100, true);
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String2", 200, false);
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String3", 300, true);

        using (StreamWriter writer = new StreamWriter("C:\\Temp\\dump.csv")) {
            Rfc4180Writer.WriteDataTable(sourceTable, writer, true);
        }
    }
} 

 ' VB Code
Public Class Program
    Public Shared Sub Main()
        Dim sourceTable As DataTable = New DataTable()
        
        sourceTable.Columns.AddRange(New DataColumn() {
            New DataColumn("ID", GetType(Guid)),
            New DataColumn("Date", GetType(Date)),
            New DataColumn("StringValue", GetType(String)),
            New DataColumn("NumberValue", GetType(Integer)),
            New DataColumn("BooleanValue", GetType(Boolean))
        })
        
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String1", 100, True)
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String2", 200, False)
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String3", 300, True)
        
        Using writer As StreamWriter = New StreamWriter("C:\Temp\dump.csv")
            Rfc4180Writer.WriteDataTable(sourceTable, writer, True)
        End Using
    End Sub
End Class  

// C# Code
public class ReportController : Controller
{
    [HttpGet()]
    public ActionResult Export()
    {
        DataTable sourceTable = new DataTable();

        sourceTable.Columns.AddRange(new DataColumn[] {
            new DataColumn("ID", typeof(Guid)),
            new DataColumn("Date", typeof(DateTime)),
            new DataColumn("StringValue", typeof(string)),
            new DataColumn("NumberValue", typeof(int)),
            new DataColumn("BooleanValue", typeof(bool))
        });

        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String1", 100, true);
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String2", 200, false);
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String3", 300, true);

        byte[] outputBuffer = null;

        using (MemoryStream tempStream = new MemoryStream()) {
            using (StreamWriter writer = new StreamWriter(tempStream)) {
                Rfc4180Writer.WriteDataTable(sourceTable, writer, true);
            }

            outputBuffer = tempStream.ToArray();
        }

        return File(outputBuffer, "text/csv", "export.csv");
    }
} 

' VB Code
Public Class ReportController
    Inherits Controller

    <HttpGet()> _
    Public Function Export() As ActionResult
        Dim sourceTable As DataTable = New DataTable()

        sourceTable.Columns.AddRange(New DataColumn() {
            New DataColumn("ID", GetType(Guid)),
            New DataColumn("Date", GetType(Date)),
            New DataColumn("StringValue", GetType(String)),
            New DataColumn("NumberValue", GetType(Integer)),
            New DataColumn("BooleanValue", GetType(Boolean))
        })

        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String1", 100, True)
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String2", 200, False)
        sourceTable.Rows.Add(Guid.NewGuid(), DateTime.Now, "String3", 300, True)

        Dim outputBuffer() As Byte = Nothing
        Using tempStream As MemoryStream = New MemoryStream()
            Using writer As StreamWriter = New StreamWriter(tempStream)
                Rfc4180Writer.WriteDataTable(sourceTable, writer, True)
            End Using

            outputBuffer = tempStream.ToArray()
        End Using

        Return File(outputBuffer, "text/csv", "export.csv")
    End Function

End Class