Simmetric.IO.Csv

.NET library for handling CSV files in various formats, including TSV, .

Why a CSV library?

I'm sure we've all written a while (streamReader.ReadLine()) { } loop a million times thinking 'CSV is easy!' and then it always turned out to be more complicated than expected, often due to text delimiters. Different separator characters, date and number formats can be a real pain, not to mention when a CSV file contains quoted text strings that may or may not contain separator characters. In that case you need more than a ReadLine() loop.

Simmetric.IO.Csv offers basic classes to read and write CSV, but also a fully functional scaffold that minimizes the code you have to write. You only have to write a class that implements ICsvRecordHandler (or ICsvSetHandler to handle more than 1 record at once) and fill in the gaps.

Usage

Format

First, it's important to know what format your CSV file is in. Otherwise all bets are off. Declare a CsvFormat object to specifiy row and column delimiters, and other options.

var format = new CsvFormat { 
   ColumnSeparator = ";",  //how are columns separated?
   LineSeparator = "\r\n", //how are lines separated? a string is allowed as input, but each character in the string separates a line on its own. this is so you can enter \r\n here
   HasHeaders = false,     //does the file have a header row?
   TextQualification       //are columns wrapped in quotes?
       = CsvFormat.TextQualificationOption.OnlyWhenNecessary, //only if a cell contains separator characters. choose this if there is no text qualification in your CSV file
   TextQualifier = '"' 
};

Handlers

A handler class takes lines of CSV and processes them. Your handler class will do the actual work such as import the CSV into a database, or convert it to a different file format.

To write a handler, implement Simmetric.IO.Csv.ICsvRecordHandler or Simmetric.IO.Csv.ICsvSetHandler. ICsvRecordHandler takes one record at a time, while ICsvSetHandler can take sets of a configurable number of records.

public class MyRecordHandler : Simmetric.IO.Csv.ICsvRecordHandler
{
    int rowNumber;
    System.Data.SqlClient.SqlConnection con;
    System.Data.SqlClient.SqlTransaction trn;

    //Called for each record in the CSV file
    public bool ProcessRecord(int recordNum, string[] fields, out string message)
    {
        //insert the data into a database table
        var com = new System.Data.SqlClient.SqlCommand("INSERT INTO table (id, name, address, city, dateofbirth) VALUES (@id, @name, @address, @city, @dateofbirth", con);
        com.Parameters.AddWithValue("@id", int.Parse(fields[0]));
        com.Parameters.AddWithValue("@name", fields[1]);
        com.Parameters.AddWithValue("@address", fields[2]);
        com.Parameters.AddWithValue("@city", fields[3]);
        com.Parameters.AddWithValue("@dateofbirth", DateTime.Parse(fields[4]));
        com.ExecuteNonQuery();

        rowNumber++;
    }

    //Called when opening a CSV file
    public void BeginProcessing(string fileName, string[] headers = null)
    {
        //initialize DB connection
        con = new System.Data.SqlClient.SqlConnection("your connectionstring here");
        con.Open();
        trn = con.BeginTransaction();
        rowNumber = 0;
    }

    //Called after the last record in the CSV file is processed
    public void EndProcessing()
    {
        //commit transaction and close DB connection
        trn.Commit();
        con.Close();
        con.Dispose();
    }

    //Called when an unhandled exception occurs. Choose whether further processing should happen.
    public string HandleRecordError(Exception ex)
    {
        //to halt further record processing, throw an exception.
        //otherwise return a sensible message that describes the error.
        trn.Rollback();
        con.Dispose();
        throw new System.Exception("Processing stopped because: " + ex.Message);
    }
}

Processing

Use the CsvProcessor to read a file, stream or string containing CSV formatted text. The processor reads the CSV and feeds each line to a handler class.

var myHandler = new MyRecordHandler();
var processor = new CsvProcessor(myHandler);
processor.ProcessFile("C:\\My Documents\\myfile.csv", format);

Reading

To simply read a CSV file row by row, use the CsvReader:

var reader = new CsvReader(fileStream, format);
while (!reader.EndOfStream)
{
   //read the CSV line by line
   IEnumerable<string> line = reader.ReadLine();
   
   //or read each cell individually
   int id = reader.ReadAsInt();
   string name = reader.Read();
   string address = reader.Read();
   string city = reader.Read();
   DateTime dateofbirth = reader.ReadAsDateTime();
   
   //read a line and return a populated object
   //note: the CSV must have headers that correspond to field names in a class
   class Person 
   {
      public int ID { get; set; }
      public string Name { get; set; }
      public string Address { get; set; }
      public string City { get; set; }
      public DateTime DateOfBirth { get; set; }
   }
   Person person = reader.ReadLine<Person>();

   //note: each Read call advances the position of the CsvReader
}

It is also possible to read a CSV file to the end and return all rows as an iterator:

var reader = new CsvReader(fileStream, format);
foreach (IEnumerable<string> line in reader.ReadToEnd())
{
   //line contains all fields as strings, just like ReadLine()
}

class Person 
{
   public int ID { get; set; }
   public string Name { get; set; }
   public string Address { get; set; }
   public string City { get; set; }
   public DateTime DateOfBirth { get; set; }
}
foreach (Person person in reader.ReadToEnd<Person>())
{
   //person is an instance of class Person
}

Writing

With the CsvWriter class you can output CSV formatted text to a stream.

using (var writer = new CsvWriter(outputStream, format))
{
 //write a string array as a line
 writer.WriteLine(new string[]{"1", "Mike O'Toole", "1234 West Street\r\n12345 Springfield NY", "Springfield", "1980-01-01"});
 //or write cells individually
 writer.Write("1");
 writer.WriteColumnSeparator();
 writer.WriteLineSeparator();
}