Patterns and Best Practices Send One Email with Attachment Instead of Multiple Emails by Les Smith

I am not going to show you any new .NET trick with this article.  Every once in a while I like to share a good programming tip that is not anything spectacular.  Rather, it is just a better way to do something that I have often done in a less than effecient or user-friendly way.  That's what this article is about; just doing a menial task of sending emails from an application in a better way.

I frequently write applications where I process large batches of input data from a client.  If for some reason a line of data does not validate, I need to send an email to the customer so that they are aware that that the line in question could not be processed.  In any case the application is designed to process the good data and bypass that which cannot be processed.

I have started with applications sending individual messages for each and every error and then found that the volume of emails could easily become a real problem, especially if the customer sends in a large number of bad input lines.  

There is a simple, but much better solution to this type of problem.  First, I create a StringBuilder object that will hold the error (or any type of anamoly) messeages during the processing of the input file.  I place the StringBuilder object at the class level so that any method in the class can see the object.  You might even globalize it further by placing it as a Publc variable in a VB.NET Module or a static varaible in a C# class.

   Private sb As New StringBuilder(5000)

Next, in the places where I determine that there is a problem with input data, etc., I add a message to the error message StringBuilder as shown below:

Dim msg As String = reason & vbCrLf & LastName & ", " & FirstName       sb.Append(msg & vbCrLf)

Finally, I have a method that is called at the end of the process to see if there were any messages created, and if so, return the filename that can be attached to a single email.  That method will write the concatenated error message to a file and return the path to the newly created file.  Note that returning an empty string means that there were no error messages created and thus no file is created.  That method is shown below.

Private Function CreateEMailAttachment() As String       If sb.Length > 0 Then          Dim fn As String = Path.Combine(logPath, "Exceptions_" & Format(Now, _             "yyyyMMddHHmmss") & ".txt")          Write2File(sb.ToString, fn)          sb = New StringBuilder(5000)          Return fn       Else          Return String.Empty       End If    End Function

When the application has completed processing, I may be sending an email to notify the customer that their file has been processed or I may only send the email if there were problems with some of the data.  In any case my email sending method will have a parameter that is the filename of the exception file.  If the name of the file parameter does not have a length of zero, then the file name will be attached to the outgoing email.  So, my call to the email method might look as follows.

SendEmail("Processing Summary" & vbCrLf & summary, EmailType.Success, _          CreateEMailAttachment())

In the SendEmail method, I will attach the file to the email if file exists.  Using this methodology in my apps guarantees that I send no more than one email regardless of the number of errors that were enumerated.  You will find that customers will like this approach much better than receiving 623 emails, each one denoting one error.

Again, not rocket science, but a better way to communicate notification of errors in a customer sent file of transactions.