csvhelper: how to write a specific "cell" on an existing csv on C#?

Question

I have a customer list in csv format which I'm using to send out emails. I would like to write to the CSV after each row has been executed in order to place a conditional rule. I'm using csvhelper to manipulate the file. Here's the code:

var scan = new StreamReader(myBlob);
var csvv = new CsvReader(scan, CultureInfo.InvariantCulture);
var records = csvv.GetRecords<Records>().ToList();
var scanwriter = new StreamWriter(myBlob4);
var csvwriter = new CsvWriter(scanwriter, CultureInfo.InvariantCulture);

foreach (Records record in records)
{
                
    var from = new EmailAddress("example.com", "John");
    var to = new EmailAddress(record.Email, record.Name);
            
    var subject = "exapmple";

    var msg = MailHelper.CreateSingleEmail(from, to, subject, txtf, htmlf);

    StringBuilder text = new StringBuilder();
    text.AppendFormat("sent", record.EmailSent);
                
    csvwriter.WriteField(record.EmailSent);
    csvwriter.NextRecord();
                
            
    var response = await client.SendEmailAsync(msg);
}

However my csv is not appending the "sent" value to the file under the emailsent column. I'm using StringBuilder which might not be helpful in this scenario.

Answer 1

It seems like you are trying to do something more like this.

void Main()
{
    var records = new List<SendEmail>
    {
        new SendEmail{ Email = "example.com", Name = "John" },
        new SendEmail{ Email = "example2.com", Name = "Jenny" }
    };
    var csvwriter = new CsvWriter(Console.Out, CultureInfo.InvariantCulture);
    
    foreach (var record in records)
    {
//      var from = new EmailAddress("example.com", "John");
//      var to = new EmailAddress(record.Email, record.Name);
//
//      var subject = "exapmple";
//
//      var msg = MailHelper.CreateSingleEmail(from, to, subject, txtf, htmlf);

        record.EmailSent = "sent";
        
        csvwriter.WriteRecord(record);
        csvwriter.NextRecord();

        //var response = await client.SendEmailAsync(msg);
    }
}

public class SendEmail
{
    public string Email { get; set; }
    public string Name { get; set; }
    public string EmailSent { get; set; }
}

Answer 2

//using blocks will make sure the streams and disposed and file handles are closed properly,
// **even if an exception is thrown **
using(var scan = new StreamReader(myBlob))
using (var csvv = new CsvReader(scan, CultureInfo.InvariantCulture))
using (var scanwriter = new StreamWriter(myBlob4))
using (var csvwriter = new CsvWriter(scanwriter, CultureInfo.InvariantCulture))
{
    var records = csvv.GetRecords<Records>(); //ToList() was not needed or helpful here
    foreach (var record in records)
    {               
        var from = new EmailAddress("example.com", "John");
        var to = new EmailAddress(record.Email, record.Name);
            
        var subject = "example";
        var msg = MailHelper.CreateSingleEmail(from, to, subject, txtf, htmlf);
                
        csvwriter.WriteField($"sent {record.EmailSent}");
        csvwriter.NextRecord();           
            
        var response = await client.SendEmailAsync(msg);
    }
}