[How to] Log into a file instead of the Error Log

Hi all, 

I share my solution to it (this still logs to the standard OS logs):

You can put it into an extender business rule as a separate namespace in this case.

Namespace Common.Logging
    Public Interface ILogging
        Sub LogTrace(message As String)
        Sub LogDebug(message As String)
        Sub LogError(message As String)
        Sub LogMessage(message As String)
    End Interface

    Public Enum LogLevel
        LogTrace = 4
        LogDebug = 3
        LogMessage = 2
        LogError = 1
    End Enum

    Public Class OneStreamLogging
        Inherits DefaultLogging

		Public Const defaultMessageHeading = "OneStreamLogging Messages"
        Private si As SessionInfo
        Private userInLoggingGroup As Boolean
        Private collectLogs As Boolean
        Private collectedLogs As New Text.StringBuilder()
		Private messageHeading As String

        Public Sub New(ByVal si As SessionInfo, Optional logLevel As LogLevel = LogLevel.LogError, Optional withTiming As Boolean = False, Optional collectLogs As Boolean = False, Optional messageHeading As String = defaultMessageHeading)
            MyBase.New(logLevel, withTiming)
            Me.si = si
            Me.collectLogs = collectLogs
            Me.userInLoggingGroup = BRApi.Security.Authorization.IsUserInGroup(si, si.UserName, "ALLC_LoggingEnabledUsers", False)
			Me.messageHeading = messageHeading
        End Sub

        Protected Overrides Sub WriteMessage(loglevel As LogLevel, message As String)
            If loglevel.Equals(LogLevel.LogError) Then
                If collectLogs Then
                    collectedLogs.AppendLine($"{loglevel}: {message}")
                Else
                    BRApi.ErrorLog.LogError(si, New XFException(message))
                End If
            Else
                If userInLoggingGroup Then
                    If collectLogs Then
                        collectedLogs.AppendLine($"{loglevel}: {message}")
                    Else
						If messageHeading.Equals(defaultMessageHeading) Then
							BRApi.ErrorLog.LogMessage(si, message)
						Else
                        	BRApi.ErrorLog.LogMessage(si, Me.messageHeading, message)
						End If
                    End If
                End If
            End If
        End Sub

        Public Sub LogCollectedLogs()
			If collectedLogs.Length > 0 Then
				If messageHeading.Equals(defaultMessageHeading) Then
					BRApi.ErrorLog.LogMessage(si, collectedLogs.ToString())
				Else
            		BRApi.ErrorLog.LogMessage(si, Me.messageHeading, collectedLogs.ToString())
				End If
			End If
        End Sub

    End Class

    Public Class DefaultLogging
        Implements ILogging

        Private desiredLogLevel As LogLevel
        Private withTiming As Boolean
        Private elapsedTime As New Stopwatch()
        Public Sub New(Optional logLevel As LogLevel = LogLevel.LogError, Optional withTiming As Boolean = False)
            Me.desiredLogLevel = logLevel
            Me.withTiming = withTiming
            If Me.withTiming Then
                elapsedTime.Start()
            End If
            Me.LogTrace("Initialized Logger")
        End Sub
        Public Sub LogTrace(message As String) Implements ILogging.LogTrace
            Log(LogLevel.LogTrace, "TRACE", message)
        End Sub

        Public Sub LogDebug(message As String) Implements ILogging.LogDebug
            Log(LogLevel.LogDebug, "DEBUG", message)
        End Sub

        Public Sub LogError(message As String) Implements ILogging.LogError
            Log(LogLevel.LogError, "ERROR", message)
        End Sub

        Public Sub LogMessage(message As String) Implements ILogging.LogMessage
            Log(LogLevel.LogMessage, "MESSAGE", message)
        End Sub

        Private Sub Log(loglevel As LogLevel, levelname As String, message As String)
            If (loglevel <= Me.desiredLogLevel) Then
                Dim stackframe As New Diagnostics.StackFrame(2)

                Dim baseFormat = $"{levelname}: {stackframe.GetMethod().DeclaringType.Namespace}:{stackframe.GetMethod().DeclaringType.Name}:{stackframe.GetMethod().Name}: "
                If withTiming Then
                    Dim ts As TimeSpan = elapsedTime.Elapsed
                    Dim formattedElapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}", ts.Hours, ts.Minutes, ts.Seconds, ts.Milliseconds / 10)
                    WriteMessage(loglevel, $"{baseFormat}: {formattedElapsedTime}: {message}")
                Else
                    WriteMessage(loglevel, $"{baseFormat}: {message}")
                End If
            End If
        End Sub

        Protected Overridable Sub WriteMessage(loglevel As LogLevel, message As String)
            Console.WriteLine(message)
        End Sub

    End Class
End Namespace

and then use e.g. like this from other BRs (of course you have to reference the above Business Rule

Imports Common.Logging

Namespace OneStream.BusinessRule.Extender.Test
	Public Class MainClass
		Public Function Main(ByVal si As SessionInfo, ByVal globals As BRGlobals, ByVal api As Object, ByVal args As DashboardStringFunctionArgs) As Object
			Dim logger As OneStreamLogging = New OneStreamLogging(si, LogLevel.LogDebug, True, True, $"Test Logging")
			Try
				logger.LogMessage("This is a message")
				logger.LogDebug("This is a debug message")
				logger.LogTrace("This is a trace massage")
				logger.LogError("This is an error message")
			Catch ex As Exception
				Throw ErrorHandler.LogWrite(si, New XFException(si, ex))
			Finally
				logger.LogCollectedLogs()
			End Try
		End Function
	End Class
End Namespace

This allows you the follwoing:

• can be used outside onestream and logs to the console
• only log for users in security group ALLC_LoggingEnabledUsers
• only log messages up to e certain log-level
• collect logs during an execution and only log everything at once on the end
• logs additional useful information / timing / stack trace /etc.

Hope that is useful to some of you

Markus