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Is there a way for extracting an Excel file from an ado.net query and adding custom columns to it using c#

I have an Excel file template, and I need to extract the data from a SQL Server database to this Excel file using C# as same as the template file.
The problem is that I need to add another column using C# to the Excel file, to make this extracted file look like the template file.
So I will not extract the Excel file's data from my web-form application directly.
I need to add some additional columns first.

Convert SQL to CSV while writing SQL result add your custom column data as well. CSV will open in excel by default.
private void SQLToCSV(string query, string Filename)
{
SqlConnection conn = new SqlConnection(connection);
conn.Open();
SqlCommand cmd = new SqlCommand(query, conn);
SqlDataReader result = cmd.ExecuteReader();
using (System.IO.StreamWriter fs = new System.IO.StreamWriter(Filename))
{
// Loop through the fields and add headers
for (int i = 0; i < result.FieldCount; i++)
{
string colval = result.GetColumnName(i);
if (colval.Contains(","))
colval = "\"" + colval + "\"";
fs.Write(colval + ",");
}
//CONCATENATE THE COLUMNS YOU WANT TO ADD IN RESULT HERE
fs.WriteLine();
// Loop through the rows and output the data
while (result.Read())
{
for (int i = 0; i < result.FieldCount; i++)
{
string value = result[i].ToString();
if (value.Contains(","))
value = "\"" + value + "\"";
fs.Write(value + ",");
}
fs.WriteLine();
}
fs.Close();
}
}
You can covert csv to excel
using Excel = Microsoft.Office.Interop.Excel;
private void Convert_CSV_To_Excel()
{
// Rename .csv To .xls
System.IO.File.Move(#"d:\Test.csv", #"d:\Test.csv.xls");
var _app = new Excel.Application();
var _workbooks = _app.Workbooks;
_workbooks.OpenText("Test.csv.xls",
DataType: Excel.XlTextParsingType.xlDelimited,
TextQualifier: Excel.XlTextQualifier.xlTextQualifierNone,
ConsecutiveDelimiter: true,
Semicolon: true);
// Convert To Excle 97 / 2003
_workbooks[1].SaveAs("NewTest.xls", Excel.XlFileFormat.xlExcel5);
_workbooks.Close();
}

Using SQLBulkCopy and IDatareader with ColumnMappings

I would like to use a DataReader considering my file has millions of lines and a DataTable seems to be slow for loading with SQLBulkCopy
I implemented this reader, which will read my file this way:
//snippet from CSVReader implementation
Read();
_csvHeaderstring = _csvlinestring;
_header = ReadRow(_csvHeaderstring);
int i = 0;
_csvHeaderstring = "";
foreach (var item in _header)//read each column and create a dummy header.
{
headercollection.Add("COL_" + i.ToString(), null);
_csvHeaderstring = _csvHeaderstring + "COL_" + i.ToString() + _delimiter;
i++;
}
_csvHeaderstring.TrimEnd(_delimiter);
_header = ReadRow(_csvHeaderstring);
Close(); //close and repoen to get the record position to beginning.
_file = File.OpenText(filePath);
public static void MyMethod()
{
textDataReader rdr = new textDataReader(file, '\t', false);
using (SqlBulkCopy bulkcopy = new SqlBulkCopy(connectionString))
{
bulkcopy.DestinationTableName = "[dbo].[MyTable]";
bulkcopy.ColumnMappings.Add("COL_0", "DestinationCol1");
bulkcopy.ColumnMappings.Add("COL_1", "DestinationCol2");
bulkcopy.ColumnMappings.Add("COL_3", "DestinationCol3");
bulkcopy.ColumnMappings.Add("COL_4", "DestinationCol4");
bulkcopy.ColumnMappings.Add("COL_5", "DestinationCol5");
bulkcopy.ColumnMappings.Add("COL_6", "DestinationCol6");
bulkcopy.WriteToServer(rdr);
bulkcopy.Close();
}
}
However when trying to do a SQLBulkCopy columnmapping to skip the unecessary column I get the error:
the given columnmapping does not match up with any column in the
source or destination.
I have also tried to map this way to no avail.
Will this implementation of IDataReader work for SQLBulkCopy? I tried implementing an 'ignore column' method but that didn't work.

How to export large SQL Server table into a CSV file using the FileHelpers library?

I'm looking to export a large SQL Server table into a CSV file using C# and the FileHelpers library.
I could consider C# and bcp as well, but I thought FileHelpers would be more flexible than bcp. Speed is not a special requirement.
OutOfMemoryException is thrown on the storage.ExtractRecords() when the below code is run (some less essential code has been omitted):
SqlServerStorage storage = new SqlServerStorage(typeof(Order));
storage.ServerName = "SqlServer";
storage.DatabaseName = "SqlDataBase";
storage.SelectSql = "select * from Orders";
storage.FillRecordCallback = new FillRecordHandler(FillRecordOrder);
Order[] output = null;
output = storage.ExtractRecords() as Order[];
When the below code is run, 'Timeout expired' is thrown on the link.ExtractToFile():
SqlServerStorage storage = new SqlServerStorage(typeof(Order));
string sqlConnectionString = "Server=SqlServer;Database=SqlDataBase;Trusted_Connection=True";
storage.ConnectionString = sqlConnectionString;
storage.SelectSql = "select * from Orders";
storage.FillRecordCallback = new FillRecordHandler(FillRecordOrder);
FileDataLink link = new FileDataLink(storage);
link.FileHelperEngine.HeaderText = headerLine;
link.ExtractToFile("file.csv");
The SQL query run takes more than the default 30 sec and therefore the timeout exception. Unfortunately, I can't find in the FileHelpers docs how to set the SQL Command timeout to a higher value.
I could consider to loop an SQL select on small data sets until the whole table gets exported, but the procedure would be too complicated.
Is there a straightforward method to use FileHelpers on large DB tables export?

Rei Sivan's answer is on the right track, as it will scale well with large files, because it avoids reading the entire table into memory. However, the code can be cleaned up.
shamp00's solution requires external libraries.
Here is a simpler table-to-CSV-file exporter that will scale well to large files, and does not require any external libraries:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Linq;
public class TableDumper
{
public void DumpTableToFile(SqlConnection connection, string tableName, string destinationFile)
{
using (var command = new SqlCommand("select * from " + tableName, connection))
using (var reader = command.ExecuteReader())
using (var outFile = File.CreateText(destinationFile))
{
string[] columnNames = GetColumnNames(reader).ToArray();
int numFields = columnNames.Length;
outFile.WriteLine(string.Join(",", columnNames));
if (reader.HasRows)
{
while (reader.Read())
{
string[] columnValues =
Enumerable.Range(0, numFields)
.Select(i => reader.GetValue(i).ToString())
.Select(field => string.Concat("\"", field.Replace("\"", "\"\""), "\""))
.ToArray();
outFile.WriteLine(string.Join(",", columnValues));
}
}
}
}
private IEnumerable<string> GetColumnNames(IDataReader reader)
{
foreach (DataRow row in reader.GetSchemaTable().Rows)
{
yield return (string)row["ColumnName"];
}
}
}
I wrote this code, and declare it CC0 (public domain).

I incorporate 2 The code above. I use this code. I use VS 2010.
//this is all lib that i used|||||||||||||||
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using UsbLibrary;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Globalization;
//cocy in a button||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SqlConnection _connection = new SqlConnection();
SqlDataAdapter _dataAdapter = new SqlDataAdapter();
SqlCommand _command = new SqlCommand();
DataTable _dataTable = new DataTable();
_connection = new SqlConnection();
_dataAdapter = new SqlDataAdapter();
_command = new SqlCommand();
_dataTable = new DataTable();
//dbk is my database name that you can change it to your database name
_connection.ConnectionString = "Data Source=.;Initial Catalog=dbk;Integrated Security=True";
_connection.Open();
SaveFileDialog saveFileDialogCSV = new SaveFileDialog();
saveFileDialogCSV.InitialDirectory = Application.ExecutablePath.ToString();
saveFileDialogCSV.Filter = "CSV files (*.csv)|*.csv|All files (*.*)|*.*";
saveFileDialogCSV.FilterIndex = 1;
saveFileDialogCSV.RestoreDirectory = true;
string path_csv="";
if (saveFileDialogCSV.ShowDialog() == DialogResult.OK)
{
// Runs the export operation if the given filenam is valid.
path_csv= saveFileDialogCSV.FileName.ToString();
}
DumpTableToFile(_connection, "tbl_trmc", path_csv);
}
//end of code in button|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
public void DumpTableToFile(SqlConnection connection, string tableName, string destinationFile)
{
using (var command = new SqlCommand("select * from " + tableName, connection))
using (var reader = command.ExecuteReader())
using (var outFile = System.IO.File.CreateText(destinationFile))
{
string[] columnNames = GetColumnNames(reader).ToArray();
int numFields = columnNames.Length;
outFile.WriteLine(string.Join(",", columnNames));
if (reader.HasRows)
{
while (reader.Read())
{
string[] columnValues =
Enumerable.Range(0, numFields)
.Select(i => reader.GetValue(i).ToString())
.Select(field => string.Concat("\"", field.Replace("\"", "\"\""), "\""))
.ToArray();
outFile.WriteLine(string.Join(",", columnValues));
}
}
}
}
private IEnumerable<string> GetColumnNames(IDataReader reader)
{
foreach (DataRow row in reader.GetSchemaTable().Rows)
{
yield return (string)row["ColumnName"];
}
}

try this one:
private void exportToCSV()
{
//Asks the filenam with a SaveFileDialog control.
SaveFileDialog saveFileDialogCSV = new SaveFileDialog();
saveFileDialogCSV.InitialDirectory = Application.ExecutablePath.ToString();
saveFileDialogCSV.Filter = "CSV files (*.csv)|*.csv|All files (*.*)|*.*";
saveFileDialogCSV.FilterIndex = 1;
saveFileDialogCSV.RestoreDirectory = true;
if (saveFileDialogCSV.ShowDialog() == DialogResult.OK)
{
// Runs the export operation if the given filenam is valid.
exportToCSVfile(saveFileDialogCSV.FileName.ToString());
}
}
* Exports data to the CSV file.
*/
private void exportToCSVfile(string fileOut)
{
// Connects to the database, and makes the select command.
string sqlQuery = "select * from dbo." + this.lbxTables.SelectedItem.ToString();
SqlCommand command = new SqlCommand(sqlQuery, objConnDB_Auto);
// Creates a SqlDataReader instance to read data from the table.
SqlDataReader dr = command.ExecuteReader();
// Retrives the schema of the table.
DataTable dtSchema = dr.GetSchemaTable();
// Creates the CSV file as a stream, using the given encoding.
StreamWriter sw = new StreamWriter(fileOut, false, this.encodingCSV);
string strRow; // represents a full row
// Writes the column headers if the user previously asked that.
if (this.chkFirstRowColumnNames.Checked)
{
sw.WriteLine(columnNames(dtSchema, this.separator));
}
// Reads the rows one by one from the SqlDataReader
// transfers them to a string with the given separator character and
// writes it to the file.
while (dr.Read())
{
strRow = "";
for (int i = 0; i < dr.FieldCount; i++)
{
switch (Convert.ToString(dr.GetFieldType(i)))
{
case "System.Int16":
strRow += Convert.ToString(dr.GetInt16(i));
break;
case "System.Int32" :
strRow += Convert.ToString(dr.GetInt32(i));
break;
case "System.Int64":
strRow += Convert.ToString(dr.GetInt64(i));
break;
case "System.Decimal":
strRow += Convert.ToString(dr.GetDecimal(i));
break;
case "System.Double":
strRow += Convert.ToString(dr.GetDouble(i));
break;
case "System.Float":
strRow += Convert.ToString(dr.GetFloat(i));
break;
case "System.Guid":
strRow += Convert.ToString(dr.GetGuid(i));
break;
case "System.String":
strRow += dr.GetString(i);
break;
case "System.Boolean":
strRow += Convert.ToString(dr.GetBoolean(i));
break;
case "System.DateTime":
strRow += Convert.ToString(dr.GetDateTime(i));
break;
}
if (i < dr.FieldCount - 1)
{
strRow += this.separator;
}
}
sw.WriteLine(strRow);
}
// Closes the text stream and the database connenction.
sw.Close();
dr.Close();
// Notifies the user.
MessageBox.Show("ready");
}

Very appreciative of Jay Sullivan's answer -- was very helpful for me.
Building on that, I observed that in his solution the string formatting of varbinary and string data types was not good -- varbinary fields would come out as literally "System.Byte" or something like that, while datetime fields would be formatted MM/dd/yyyy hh:mm:ss tt, which is not desirable for me.
Below I is my hacked-together solution which converts to string differently based on data type. It is uses nested ternary operators, but it works!
Hope it is helpful for someone.
public static void DumpTableToFile(SqlConnection connection, Dictionary<string, string> cArgs)
{
string query = "SELECT ";
string z = "";
if (cArgs.TryGetValue("top_count", out z))
{
query += string.Format("TOP {0} ", z);
}
query += string.Format("* FROM {0} (NOLOCK) ", cArgs["table"]);
string lower_bound = "", upper_bound = "", column_name = "";
if (cArgs.TryGetValue("lower_bound", out lower_bound) && cArgs.TryGetValue("column_name", out column_name))
{
query += string.Format("WHERE {0} >= {1} ", column_name, lower_bound);
if (cArgs.TryGetValue("upper_bound", out upper_bound))
{
query += string.Format("AND {0} < {1} ", column_name, upper_bound);
}
}
Console.WriteLine(query);
Console.WriteLine("");
using (var command = new SqlCommand(query, connection))
using (var reader = command.ExecuteReader())
using (var outFile = File.CreateText(cArgs["out_file"]))
{
string[] columnNames = GetColumnNames(reader).ToArray();
int numFields = columnNames.Length;
Console.WriteLine(string.Join(",", columnNames));
Console.WriteLine("");
if (reader.HasRows)
{
Type datetime_type = Type.GetType("System.DateTime");
Type byte_arr_type = Type.GetType("System.Byte[]");
string format = "yyyy-MM-dd HH:mm:ss.fff";
int ii = 0;
while (reader.Read())
{
ii += 1;
string[] columnValues =
Enumerable.Range(0, numFields)
.Select(i => reader.GetValue(i).GetType()==datetime_type?((DateTime) reader.GetValue(i)).ToString(format):(reader.GetValue(i).GetType() == byte_arr_type? String.Concat(Array.ConvertAll((byte[]) reader.GetValue(i), x => x.ToString("X2"))) :reader.GetValue(i).ToString()))
///.Select(field => string.Concat("\"", field.Replace("\"", "\"\""), "\""))
.Select(field => field.Replace("\t", " "))
.ToArray();
outFile.WriteLine(string.Join("\t", columnValues));
if (ii % 100000 == 0)
{
Console.WriteLine("row {0}", ii);
}
}
}
}
}
public static IEnumerable<string> GetColumnNames(IDataReader reader)
{
foreach (DataRow row in reader.GetSchemaTable().Rows)
{
yield return (string)row["ColumnName"];
}
}

FileHelpers has an async engine which is better suited for handling large files. Unfortunately, the FileDataLink class does not use it, so there's no easy way to use it with SqlStorage.
It's not very easy to modify the SQL timeout either. The easiest way would be to copy the code for SqlServerStorage to create your own alternative storage provider and provide replacements for ExecuteAndClose() and ExecuteAndLeaveOpen() which set the timeout on the IDbCommand. (SqlServerStorage is a sealed class, so you cannot just subclass it).
You might want to check out ReactiveETL which uses the FileHelpers async engine for handling files along with a rewrite of Ayende's RhinoETL using ReactiveExtensions to handle large datasets.

Reading/writing CSV/tab delimited files in c#

I need to read from a CSV/Tab delimited file and write to such a file as well from .net.
The difficulty is that I don't know the structure of each file and need to write the cvs/tab file to a datatable, which the FileHelpers library doesn't seem to support.
I've already written it for Excel using OLEDB, but can't really see a way to write a tab file for this, so will go back to a library.
Can anyone help with suggestions?

.NET comes with a CSV/tab delminited file parser called the TextFieldParser class.
http://msdn.microsoft.com/en-us/library/microsoft.visualbasic.fileio.textfieldparser.aspx
It supports the full RFC for CSV files and really good error reporting.

I used this CsvReader, it is really great and well configurable. It behaves well with all kinds of escaping for strings and separators. The escaping in other quick and dirty implementations were poor, but this lib is really great at reading. With a few additional codelines you can also add a cache if you need to.
Writing is not supported but it rather trivial to implement yourself. Or inspire yourself from this code.

Simple example with CsvHelper
using (TextWriter writer = new StreamWriter(filePath)
{
var csvWriter = new CsvWriter(writer);
csvWriter.Configuration.Delimiter = "\t";
csvWriter.Configuration.Encoding = Encoding.UTF8;
csvWriter.WriteRecords(exportRecords);
}

Here are a couple CSV reader implementations:
http://www.codeproject.com/KB/database/CsvReader.aspx
http://www.heikniemi.fi/jhlib/ (just one part of the library; includes a CSV writer too)
I doubt there is a standard way to convert CSV to DataTable or database 'automatically', you'll have to write code to do that. How to do that is a separate question.

You'll create your datatable in code, and (presuming a header row) can create columns based on your first line in the file. After that, it will simply be a matter of reading the file and creating new rows based on the data therein.
You could use something like this:
DataTable Tbl = new DataTable();
using(StreamReader sr = new StreamReader(path))
{
int count = 0;
string headerRow = sr.Read();
string[] headers = headerRow.split("\t") //Or ","
foreach(string h in headers)
{
DataColumn dc = new DataColumn(h);
Tbl.Columns.Add(dc);
count++;
}
while(sr.Peek())
{
string data = sr.Read();
string[] cells = data.Split("\t")
DataRow row = new DataRow();
foreach(string c in cells)
{
row.Columns.Add(c);
}
Tbl.Rows.Add(row);
}
}
The above code has not been compiled, so it may have some errors, but it should get you on the right track.

You can read and write csv file..
This may be helpful for you.
pass split char to this parameter "serparationChar"
Example : -
private DataTable dataTable = null;
private bool IsHeader = true;
private string headerLine = string.Empty;
private List<string> AllLines = new List<string>();
private StringBuilder sb = new StringBuilder();
private char seprateChar = ',';
public DataTable ReadCSV(string path, bool IsReadHeader, char serparationChar)
{
seprateChar = serparationChar;
IsHeader = IsReadHeader;
using (StreamReader sr = new StreamReader(path,Encoding.Default))
{
while (!sr.EndOfStream)
{
AllLines.Add( sr.ReadLine());
}
createTemplate(AllLines);
}
return dataTable;
}
public void WriteCSV(string path,DataTable dtable,char serparationChar)
{
AllLines = new List<string>();
seprateChar = serparationChar;
List<string> StableHeadrs = new List<string>();
int colCount = 0;
using (StreamWriter sw = new StreamWriter(path))
{
foreach (DataColumn col in dtable.Columns)
{
sb.Append(col.ColumnName);
if(dataTable.Columns.Count-1 > colCount)
sb.Append(seprateChar);
colCount++;
}
AllLines.Add(sb.ToString());
for (int i = 0; i < dtable.Rows.Count; i++)
{
sb.Clear();
for (int j = 0; j < dtable.Columns.Count; j++)
{
sb.Append(Convert.ToString(dtable.Rows[i][j]));
if (dataTable.Columns.Count - 1 > j)
sb.Append(seprateChar);
}
AllLines.Add(sb.ToString());
}
foreach (string dataline in AllLines)
{
sw.WriteLine(dataline);
}
}
}
private DataTable createTemplate(List<string> lines)
{
List<string> headers = new List<string>();
dataTable = new DataTable();
if (lines.Count > 0)
{
string[] argHeaders = null;
for (int i = 0; i < lines.Count; i++)
{
if (i > 0)
{
DataRow newRow = dataTable.NewRow();
// others add to rows
string[] argLines = lines[i].Split(seprateChar);
for (int b = 0; b < argLines.Length; b++)
{
newRow[b] = argLines[b];
}
dataTable.Rows.Add(newRow);
}
else
{
// header add to columns
argHeaders = lines[0].Split(seprateChar);
foreach (string c in argHeaders)
{
DataColumn column = new DataColumn(c, typeof(string));
dataTable.Columns.Add(column);
}
}
}
}
return dataTable;
}

I have found best solution
http://www.codeproject.com/Articles/415732/Reading-and-Writing-CSV-Files-in-Csharp
Just I had to re-write
void ReadTest()
{
// Read sample data from CSV file
using (CsvFileReader reader = new CsvFileReader("ReadTest.csv"))
{
CsvRow row = new CsvRow();
while (reader.ReadRow(row))
{
foreach (string s in row)
{
Console.Write(s);
Console.Write(" ");
}
Console.WriteLine();
row = new CsvRow(); //this line added
}
}
}

Well, there is another library Cinchoo ETL - an open source one, for reading and writing CSV files.
Couple of ways you can read CSV files
Id, Name
1, Tom
2, Mark
This is how you can use this library to read it
using (var reader = new ChoCSVReader("emp.csv").WithFirstLineHeader())
{
foreach (dynamic item in reader)
{
Console.WriteLine(item.Id);
Console.WriteLine(item.Name);
}
}
If you have POCO object defined to match up with CSV file like below
public class Employee
{
public int Id { get; set; }
public string Name { get; set; }
}
You can parse the same file using this POCO class as below
using (var reader = new ChoCSVReader<Employee>("emp.csv").WithFirstLineHeader())
{
foreach (var item in reader)
{
Console.WriteLine(item.Id);
Console.WriteLine(item.Name);
}
}
Please check out articles at CodeProject on how to use it.
Disclaimer: I'm the author of this library

Exporting the values in List to excel

Hi I am having a list container which contains the list of values. I wish to export the list values directly to Excel. Is there any way to do it directly?

OK, here is a step-by-step guide if you want to use COM.
You have to have Excel installed.
Add a reference to your project to the excel interop dll. To do this
on the .NET tab select
Microsoft.Office.Interop.Excel.
There could be multiple assemblies
with this name. Select the
appropriate for your Visual Studio
AND Excel version.
Here is a code sample to create a new Workbook and fill a column with
the items from your list.
using NsExcel = Microsoft.Office.Interop.Excel;
public void ListToExcel(List<string> list)
{
//start excel
NsExcel.ApplicationClass excapp = new Microsoft.Office.Interop.Excel.ApplicationClass();
//if you want to make excel visible
excapp.Visible = true;
//create a blank workbook
var workbook = excapp.Workbooks.Add(NsExcel.XlWBATemplate.xlWBATWorksheet);
//or open one - this is no pleasant, but yue're probably interested in the first parameter
string workbookPath = "C:\test.xls";
var workbook = excapp.Workbooks.Open(workbookPath,
0, false, 5, "", "", false, Excel.XlPlatform.xlWindows, "",
true, false, 0, true, false, false);
//Not done yet. You have to work on a specific sheet - note the cast
//You may not have any sheets at all. Then you have to add one with NsExcel.Worksheet.Add()
var sheet = (NsExcel.Worksheet)workbook.Sheets[1]; //indexing starts from 1
//do something usefull: you select now an individual cell
var range = sheet.get_Range("A1", "A1");
range.Value2 = "test"; //Value2 is not a typo
//now the list
string cellName;
int counter = 1;
foreach (var item in list)
{
cellName = "A" + counter.ToString();
var range = sheet.get_Range(cellName, cellName);
range.Value2 = item.ToString();
++counter;
}
//you've probably got the point by now, so a detailed explanation about workbook.SaveAs and workbook.Close is not necessary
//important: if you did not make excel visible terminating your application will terminate excel as well - I tested it
//but if you did it - to be honest - I don't know how to close the main excel window - maybee somewhere around excapp.Windows or excapp.ActiveWindow
}

Using ClosedXML edit library( there is no need to install MS Excel
I just write a simple example to show you how you can name the file, the worksheet and select cells:
var workbook = new XLWorkbook();
workbook.AddWorksheet("sheetName");
var ws = workbook.Worksheet("sheetName");
int row = 1;
foreach (object item in itemList)
{
ws.Cell("A" + row.ToString()).Value = item.ToString();
row++;
}
workbook.SaveAs("yourExcel.xlsx");
If you prefer you can create a System.Data.DataSet or a System.Data.DataTable with all data and then just add it as a workseet with workbook.AddWorksheet(yourDataset) or workbook.AddWorksheet(yourDataTable);

Using the CSV idea, if it's just a list of Strings. Assuming l is your list:
using System.IO;
using(StreamWriter sw = File.CreateText("list.csv"))
{
for(int i = 0; i < l.Count; i++)
{
sw.WriteLine(l[i]);
}
}

Fast way - ArrayToExcel (github)
byte[] excel = myList.ToExcel();
File.WriteAllBytes("result.xlsx", excel);

The simplest way using ClosedXml.
Imports ClosedXML.Excel
var dataList = new List<string>() { "a", "b", "c" };
var workbook = new XLWorkbook(); //creates the workbook
var wsDetailedData = workbook.AddWorksheet("data"); //creates the worksheet with sheetname 'data'
wsDetailedData.Cell(1, 1).InsertTable(dataList); //inserts the data to cell A1 including default column name
workbook.SaveAs(#"C:\data.xlsx"); //saves the workbook
For more info, you can also check wiki of ClosedXml.
https://github.com/closedxml/closedxml/wiki

Exporting values List to Excel
Install in nuget next reference
Install-Package Syncfusion.XlsIO.Net.Core -Version 17.2.0.35
Install-Package ClosedXML -Version 0.94.2
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ClosedXML;
using ClosedXML.Excel;
using Syncfusion.XlsIO;
namespace ExporteExcel
{
class Program
{
public class Auto
{
public string Marca { get; set; }
public string Modelo { get; set; }
public int Ano { get; set; }
public string Color { get; set; }
public int Peronsas { get; set; }
public int Cilindros { get; set; }
}
static void Main(string[] args)
{
//Lista Estatica
List<Auto> Auto = new List<Program.Auto>()
{
new Auto{Marca = "Chevrolet", Modelo = "Sport", Ano = 2019, Color= "Azul", Cilindros=6, Peronsas= 4 },
new Auto{Marca = "Chevrolet", Modelo = "Sport", Ano = 2018, Color= "Azul", Cilindros=6, Peronsas= 4 },
new Auto{Marca = "Chevrolet", Modelo = "Sport", Ano = 2017, Color= "Azul", Cilindros=6, Peronsas= 4 }
};
//Inizializar Librerias
var workbook = new XLWorkbook();
workbook.AddWorksheet("sheetName");
var ws = workbook.Worksheet("sheetName");
//Recorrer el objecto
int row = 1;
foreach (var c in Auto)
{
//Escribrie en Excel en cada celda
ws.Cell("A" + row.ToString()).Value = c.Marca;
ws.Cell("B" + row.ToString()).Value = c.Modelo;
ws.Cell("C" + row.ToString()).Value = c.Ano;
ws.Cell("D" + row.ToString()).Value = c.Color;
ws.Cell("E" + row.ToString()).Value = c.Cilindros;
ws.Cell("F" + row.ToString()).Value = c.Peronsas;
row++;
}
//Guardar Excel
//Ruta = Nombre_Proyecto\bin\Debug
workbook.SaveAs("Coches.xlsx");
}
}
}

You could output them to a .csv file and open the file in excel. Is that direct enough?

The most straightforward way (in my opinion) would be to simply put together a CSV file. If you want to get into formatting and actually writing to a *.xlsx file, there are more complicated solutions (and APIs) to do that for you.

the one easy way to do it is to open Excel create sheet containing test data you want to export then say to excel save as xml open the xml see the xml format excel is expecting and generate it by head replacing the test data with export data
SpreadsheetML Markup Spec
#lan this is xml fo a simle execel file with one column value i genereted with office 2003 this format is for office 2003 and above
<?xml version="1.0"?>
<?mso-application progid="Excel.Sheet"?>
<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"
xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:x="urn:schemas-microsoft-com:office:excel"
xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet"
xmlns:html="http://www.w3.org/TR/REC-html40">
<DocumentProperties xmlns="urn:schemas-microsoft-com:office:office">
<Author>Dancho</Author>
<LastAuthor>Dancho</LastAuthor>
<Created>2010-02-05T10:15:54Z</Created>
<Company>cc</Company>
<Version>11.9999</Version>
</DocumentProperties>
<ExcelWorkbook xmlns="urn:schemas-microsoft-com:office:excel">
<WindowHeight>13800</WindowHeight>
<WindowWidth>24795</WindowWidth>
<WindowTopX>480</WindowTopX>
<WindowTopY>105</WindowTopY>
<ProtectStructure>False</ProtectStructure>
<ProtectWindows>False</ProtectWindows>
</ExcelWorkbook>
<Styles>
<Style ss:ID="Default" ss:Name="Normal">
<Alignment ss:Vertical="Bottom"/>
<Borders/>
<Font/>
<Interior/>
<NumberFormat/>
<Protection/>
</Style>
</Styles>
<Worksheet ss:Name="Sheet1">
<Table ss:ExpandedColumnCount="1" ss:ExpandedRowCount="6" x:FullColumns="1"
x:FullRows="1">
<Row>
<Cell><Data ss:Type="String">Value1</Data></Cell>
</Row>
<Row>
<Cell><Data ss:Type="String">Value2</Data></Cell>
</Row>
<Row>
<Cell><Data ss:Type="String">Value3</Data></Cell>
</Row>
<Row>
<Cell><Data ss:Type="String">Value4</Data></Cell>
</Row>
<Row>
<Cell><Data ss:Type="String">Value5</Data></Cell>
</Row>
<Row>
<Cell><Data ss:Type="String">Value6</Data></Cell>
</Row>
</Table>
<WorksheetOptions xmlns="urn:schemas-microsoft-com:office:excel">
<Selected/>
<Panes>
<Pane>
<Number>3</Number>
<ActiveRow>5</ActiveRow>
</Pane>
</Panes>
<ProtectObjects>False</ProtectObjects>
<ProtectScenarios>False</ProtectScenarios>
</WorksheetOptions>
</Worksheet>
<Worksheet ss:Name="Sheet2">
<WorksheetOptions xmlns="urn:schemas-microsoft-com:office:excel">
<ProtectObjects>False</ProtectObjects>
<ProtectScenarios>False</ProtectScenarios>
</WorksheetOptions>
</Worksheet>
<Worksheet ss:Name="Sheet3">
<WorksheetOptions xmlns="urn:schemas-microsoft-com:office:excel">
<ProtectObjects>False</ProtectObjects>
<ProtectScenarios>False</ProtectScenarios>
</WorksheetOptions>
</Worksheet>
</Workbook>

Depending on the environment you're wanting to do this in, it is possible by using the Excel Interop. It's quite a mess dealing with COM however and ensuring you clear up resources else Excel instances stay hanging around on your machine.
Checkout this MSDN Example if you want to learn more.
Depending on your format you could produce CSV or SpreadsheetML yourself, thats not too hard. Other alternatives are to use 3rd party libraries to do it. Obviously they cost money though.

List<"classname"> getreport = cs.getcompletionreport();
var getreported = getreport.Select(c => new { demographic = c.rName);
where cs.getcompletionreport() reference class file is Business Layer for App
I hope this helps.

I know, I am late to this party, however I think it could be helpful for others.
Already posted answers are for csv and other one is by Interop dll where you need to install excel over the server, every approach has its own pros and cons.
Here is an option which will give you
Perfect excel output [not csv]
With perfect excel and your data type match
Without excel installation
Pass list and get Excel output :)
you can achieve this by using NPOI DLL, available for both .net as well as for .net core
Steps :
Import NPOI DLL
Add Section 1 and 2 code provided below
Good to go
Section 1
This code performs below task :
Creating New Excel object - _workbook = new XSSFWorkbook();
Creating New Excel Sheet object - _sheet =_workbook.CreateSheet(_sheetName);
Invokes WriteData() - explained later Finally, creating and
returning MemoryStream object
=============================================================================
using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
namespace GenericExcelExport.ExcelExport
{
public interface IAbstractDataExport
{
HttpResponseMessage Export(List exportData, string fileName, string sheetName);
}
public abstract class AbstractDataExport : IAbstractDataExport
{
protected string _sheetName;
protected string _fileName;
protected List _headers;
protected List _type;
protected IWorkbook _workbook;
protected ISheet _sheet;
private const string DefaultSheetName = "Sheet1";
public HttpResponseMessage Export
(List exportData, string fileName, string sheetName = DefaultSheetName)
{
_fileName = fileName;
_sheetName = sheetName;
_workbook = new XSSFWorkbook(); //Creating New Excel object
_sheet = _workbook.CreateSheet(_sheetName); //Creating New Excel Sheet object
var headerStyle = _workbook.CreateCellStyle(); //Formatting
var headerFont = _workbook.CreateFont();
headerFont.IsBold = true;
headerStyle.SetFont(headerFont);
WriteData(exportData); //your list object to NPOI excel conversion happens here
//Header
var header = _sheet.CreateRow(0);
for (var i = 0; i < _headers.Count; i++)
{
var cell = header.CreateCell(i);
cell.SetCellValue(_headers[i]);
cell.CellStyle = headerStyle;
}
for (var i = 0; i < _headers.Count; i++)
{
_sheet.AutoSizeColumn(i);
}
using (var memoryStream = new MemoryStream()) //creating memoryStream
{
_workbook.Write(memoryStream);
var response = new HttpResponseMessage(HttpStatusCode.OK)
{
Content = new ByteArrayContent(memoryStream.ToArray())
};
response.Content.Headers.ContentType = new MediaTypeHeaderValue
("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
response.Content.Headers.ContentDisposition =
new ContentDispositionHeaderValue("attachment")
{
FileName = $"{_fileName}_{DateTime.Now.ToString("yyyyMMddHHmmss")}.xlsx"
};
return response;
}
}
//Generic Definition to handle all types of List
public abstract void WriteData(List exportData);
}
}
=============================================================================
Section 2
In section 2, we will be performing below steps :
Converts List to DataTable Reflection to read property name, your
Column header will be coming from here
Loop through DataTable to Create excel Rows
=============================================================================
using NPOI.SS.UserModel;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Text.RegularExpressions;
namespace GenericExcelExport.ExcelExport
{
public class AbstractDataExportBridge : AbstractDataExport
{
public AbstractDataExportBridge()
{
_headers = new List<string>();
_type = new List<string>();
}
public override void WriteData<T>(List<T> exportData)
{
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(typeof(T));
DataTable table = new DataTable();
foreach (PropertyDescriptor prop in properties)
{
var type = Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType;
_type.Add(type.Name);
table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ??
prop.PropertyType);
string name = Regex.Replace(prop.Name, "([A-Z])", " $1").Trim(); //space separated
//name by caps for header
_headers.Add(name);
}
foreach (T item in exportData)
{
DataRow row = table.NewRow();
foreach (PropertyDescriptor prop in properties)
row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
table.Rows.Add(row);
}
IRow sheetRow = null;
for (int i = 0; i < table.Rows.Count; i++)
{
sheetRow = _sheet.CreateRow(i + 1);
for (int j = 0; j < table.Columns.Count; j++)
{
ICell Row1 = sheetRow.CreateCell(j);
string type = _type[j].ToLower();
var currentCellValue = table.Rows[i][j];
if (currentCellValue != null &&
!string.IsNullOrEmpty(Convert.ToString(currentCellValue)))
{
if (type == "string")
{
Row1.SetCellValue(Convert.ToString(currentCellValue));
}
else if (type == "int32")
{
Row1.SetCellValue(Convert.ToInt32(currentCellValue));
}
else if (type == "double")
{
Row1.SetCellValue(Convert.ToDouble(currentCellValue));
}
}
else
{
Row1.SetCellValue(string.Empty);
}
}
}
}
}
}
=============================================================================
Now you just need to call
WriteData() function by passing your list, and it will provide you your excel.
I have tested it in WEB API and WEB API Core, works like a charm.

Pass List to "Write" Method, which will convert the list to buffer and return buffer, a file will be downloaded
byte[] buffer = Write(ListData, true, "AttendenceSummary"); return File(buffer, "application/excel", reportTitle + ".xlsx");
public static byte[] Write<T>(IEnumerable<T> list, bool xlsxExtension, string sheetName = "ExportData")
{
if (list == null)
{
throw new ArgumentNullException("list");
}
XSSFWorkbook hssfworkbook = new XSSFWorkbook();
int Rowspersheet = 15000;
int TotalRows = list.Count();
int TotalSheets = TotalRows / Rowspersheet;
for (int i = 0; i <= TotalSheets; i++)
{
ISheet sheet1 = hssfworkbook.CreateSheet(sheetName + "_" + i);
IRow row = sheet1.CreateRow(0);
int index = 0;
foreach (PropertyInfo property in typeof(T).GetProperties())
{
ICellStyle cellStyle = hssfworkbook.CreateCellStyle();
IFont cellFont = hssfworkbook.CreateFont();
cellFont.Boldweight = (short)NPOI.SS.UserModel.FontBoldWeight.Bold;
cellStyle.SetFont(cellFont);
ICell cell = row.CreateCell(index++);
cell.CellStyle = cellStyle;
cell.SetCellValue(property.Name);
}
int rowIndex = 1;
// int rowIndex2 = 1;
foreach (T obj in list.Skip(Rowspersheet * i).Take(Rowspersheet))
{
row = sheet1.CreateRow(rowIndex++);
index = 0;
foreach (PropertyInfo property in typeof(T).GetProperties())
{
ICell cell = row.CreateCell(index++);
cell.SetCellValue(Convert.ToString(property.GetValue(obj)));
}
}
}
MemoryStream file = new MemoryStream();
hssfworkbook.Write(file);
return file.ToArray();
}