OneStream – Error messages with debug information

One of the frustrations of coding VB.NET in OneStream is that while the error messages contain a lot of information only the first line or so is useful (and that is putting a positive spin on it). Consequently we tend to add debug information which is printed to the error log and then commented out or removed when the script goes live. Sometimes you will see a debug flag to control whether to print these messages to the log. I think that is a bit messy; first of all you get a load of messages in the log and secondly if the script is already in production there might be audit problems, you might not have access etc.

With all that in mind, I decided to see if I could find a better way of presenting more information when an error occurs. I wanted a method that gave me more information about what was happening when the error occurred, did not fill up the error log with messages, was easy to manage and did not have a large impact on performance.

The way I now code a script is:
1. Create a variable that will hold debug information: eg Dim CurrentPosition as String
This variable must be created BEFORE the Try block.
2. Update this variable through the script eg CurrentPosition = “Getting the XFFolderEx object…”
3. Write that to the error log eg BRApi.ErrorLog.LogMessage(si, CurrentPosition)

The next step is to add this ‘CurrentPosition’ information to any errors that are thrown. I do that by creating a new instance of the exception object and add the CurrentPosition variable to the end of the exception message:

Catch ex As Exception
    Dim MHEx As Exception = Activator.CreateInstance(ex.GetType(), ex.Message & Environment.NewLine & "ProcName ERROR - Position: " & CurrentPosition & Environment.NewLine, ex)
    Throw ErrorHandler.LogWrite(si, New XFException(si, MHex))

When the script is working I then comment out all the lines that print to the error log leaving the variable assignments in place.

Here is a simple example. This piece of code will throw an error because the script is trying to insert a value too large for the int16 variable:

Dim varNoDaysSmall As Int16 = 10
Dim varNoDaysLarge As Integer = 1000

For tempNumber As Int16 = 1 To 10
  varNoDaysSmall *= tempNumber
  varNoDaysLarge *= tempNumber
Next

This is the error you get (running from an Extender type Rule):

Now add the CurrentPosition debug information and the updated exception message:

For tempNumber As Int16 = 1 To 10
  CurrentPosition = String.Format("varNoDaysSmall value [{0}] tempNumber [{1}]", varNoDaysSmall.ToString, tempNumber.ToString)
  varNoDaysSmall *= tempNumber
  CurrentPosition = String.Format("varNoDaysLarge value [{0}] tempNumber [{1}]", varNoDaysLarge.ToString, tempNumber.ToString)
  varNoDaysLarge *= tempNumber
Next

And this is the error message you get:

This is just a simple example of getting debug information into an error message. No logs in the error log, very little overhead, simple to implement. I hope you find it useful – over the past few months it has saved me a huge amount of time debugging errors.

Here is the full demo script:

Public Function Main(ByVal si As SessionInfo, ByVal globals As BRGlobals, ByVal api As Object, ByVal args As ExtenderArgs) As Object
  Dim CurrentPosition As String = "Start"
  Try
    Dim varNoDaysSmall As Int16 = 10
    Dim varNoDaysLarge As Integer = 1000

    For tempNumber As Int16 = 1 To 10
      CurrentPosition = String.Format("varNoDaysSmall value [{0}]", varNoDaysSmall.ToString)
      varNoDaysSmall *= tempNumber
      CurrentPosition = String.Format("varNoDaysLarge value [{0}]", varNoDaysLarge.ToString)
      varNoDaysLarge *= tempNumber
    Next

  Catch ex As Exception
    Dim MHEx As Exception = Activator.CreateInstance(ex.GetType(), ex.Message & Environment.NewLine & "DemoError ERROR - Position: " & CurrentPosition & Environment.NewLine, ex)
    Throw ErrorHandler.LogWrite(si, New XFException(si, MHex))

  End Try
End Function

• OneStream
• Script