Creating an Audit Trail (Source Code)

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by Allen Browne, 15 May 2008    (Access 97+)

Code to accompany the Audit Log article.


' Author:   Allen Browne, allen@allenbrowne.com, 2006.

' Purpose:  Audit trail, to track Deletes, Edits, and Inserts.
'           Does not audit any Cascading Updates/Deletes.

' Requirements: The table to be audited must have an AutoNumber primary key.
'               Data entry must be through a form.

' Method:   Makes a copy of the record in a temp table, and logs the
'           change when it is guaranteed. The temp table copes with:
'               - multiple deletes at once (continuous/datasheet view)
'               - cancelled deletes or failed updates.
'               - requirement for sequential numbering in the audit table.
'           On a multi-user split (front-end/back-end) database, the
'           temp table may reside in the front end, and the audit log
'           in the back-end.

' Result:   The audit table will contain one record for each deletion or
'           insertion, and two records for each edit (before and after).
'               Delete Copy of the deleted record, marked "Delete".
'               Insert Copy of the new record, marked "Insert".
'               Change: Copy of the record before change, marked "EditFrom".
'               Copy of the record after change, marked "EditTo".
'           This approach, together with the sequential numbering of the
'           AutoNumber in the audit table makes tampering with the audit
'           log more detectable.

'Note:      Record confirmations need to be on. When opening the database:
'               If Not Application.GetOption("Confirm Record Changes") Then
'                   Application.SetOption ("Confirm Record Changes"), True
'               End If

Option Compare Database
Option Explicit

Private Const conMod As String = "ajbAudit"
Private Declare Function apiGetUserName Lib "advapi32.dll" Alias _
    "GetUserNameA" (ByVal lpBuffer As String, nSize As Long) As Long


Function NetworkUserName() As String
'On Error GoTo Err_Handler
    'Purpose:    Returns the network login name
    Dim lngLen As Long
    Dim lngX As Long
    Dim strUserName As String

    NetworkUserName = "Unknown"

    strUserName = String$(254, 0)
    lngLen = 255&
    lngX = apiGetUserName(strUserName, lngLen)
    If (lngX > 0&) Then
        NetworkUserName = Left$(strUserName, lngLen - 1&)
    End If

Exit_Handler:
    Exit Function

Err_Handler:
    Call LogError(Err.Number, Err.Description, conMod & ".NetworkUserName", , False)
    Resume Exit_Handler
End Function


Function AuditDelBegin(sTable As String, sAudTmpTable As String, sKeyField As String, lngKeyValue As Long) As Boolean
'On Error GoTo Err_AuditDelBegin
    'Purpose:    Write a copy of the record to a tmp audit table.
    '            Copy to be written to real audit table in AfterDelConfirm.
    'Arguments:  sTable = name of table to be audited.
    '            sAudTmpTable = the name of the temp audit table.
    '            sKeyField = name of AutoNumber field in table.
    '            lngKeyValue = number in the AutoNumber field.
    'Return:     True if successful.
    'Usage:      Call from a form's Delete event. Example:
    '                Call AuditDelBegin("tblInvoice", "audTmpInvoice", "InvoiceID", Me.InvoiceID)
    'Note:       Must also call AuditDelEnd in the form's AfterDelConfirm event.
    Dim db As DAO.Database           ' Current database
    Dim sSQL As String               ' Append query.

    ' Append record to the temp audit table.
    Set db = DBEngine(0)(0)
    sSQL = "INSERT INTO " & sAudTmpTable & " ( audType, audDate, audUser ) " & _
        "SELECT 'Delete' AS Expr1, Now() AS Expr2, NetworkUserName() AS Expr3, " & sTable & ".* " & _
        "FROM " & sTable & " WHERE (" & sTable & "." & sKeyField & " = " & lngKeyValue & ");"
    db.Execute sSQL, dbFailOnError

Exit_AuditDelBegin:
    Set db = Nothing
    Exit Function

Err_AuditDelBegin:
    Call LogError(Err.Number, Err.Description, conMod & ".AuditDelBegin()", , False)
    Resume Exit_AuditDelBegin
End Function


Function AuditDelEnd(sAudTmpTable As String, sAudTable As String, Status As Integer) As Boolean
'On Error GoTo Err_AuditDelEnd
    'Purpose:    If the deletion was completed, copy the data from the
    '                temp table to the autit table. Empty temp table.
    'Arguments:  sAudTmpTable = name of temp audit table
    '            sAudTable = name of audit table
    '            Status = Status from the form's AfterDelConfirm event.
    'Return:     True if successful.
    'Usage:      Call from form's AfterDelConfirm event. Example:
    '                Call AuditDelEnd("audTmpInvoice", "audInvoice", Status)
    Dim db As DAO.Database           ' Currrent database
    Dim sSQL As String               ' Append query.

    ' If the Delete proceeded, copy the record(s) from temp table to delete table.
    ' Note: Only "Delete" types are copied: cancelled Edits may be there as well.
    Set db = DBEngine(0)(0)
    If Status = acDeleteOK Then
        sSQL = "INSERT INTO " & sAudTable & " SELECT " & sAudTmpTable & ".* FROM " & sAudTmpTable & _
            " WHERE (" & sAudTmpTable & ".audType = 'Delete');"
        db.Execute sSQL, dbFailOnError
    End If

    'Remove the temp record(s).
    sSQL = "DELETE FROM " & sAudTmpTable & ";"
    db.Execute sSQL, dbFailOnError
    AuditDelEnd = True

Exit_AuditDelEnd:
    Set db = Nothing
    Exit Function

Err_AuditDelEnd:
    Call LogError(Err.Number, Err.Description, conMod & ".AuditDelEnd()", False)
    Resume Exit_AuditDelEnd
End Function


Function AuditEditBegin(sTable As String, sAudTmpTable As String, sKeyField As String, _
    lngKeyValue As Long, bWasNewRecord As Boolean) As Boolean
'On Error GoTo Err_AuditEditBegin
    'Purpose:    Write a copy of the old values to temp table.
    '            It is then copied to the true audit table in AuditEditEnd.
    'Arugments:  sTable = name of table being audited.
    '            sAudTmpTable = name of the temp audit table.
    '            sKeyField = name of the AutoNumber field.
    '            lngKeyValue = Value of the AutoNumber field.
    '            bWasNewRecord = True if this was a new insert.
    'Return:     True if successful
    'Usage:      Called in form's BeforeUpdate event. Example:
    '                bWasNewRecord = Me.NewRecord
    '                Call AuditEditBegin("tblInvoice", "audTmpInvoice", "InvoiceID", Me.InvoiceID, bWasNewRecord)
    Dim db As DAO.Database           ' Current database
    Dim sSQL As String

    'Remove any cancelled update still in the tmp table.
    Set db = DBEngine(0)(0)
    sSQL = "DELETE FROM " & sAudTmpTable & ";"
    db.Execute sSQL

    ' If this was not a new record, save the old values.
    If Not bWasNewRecord Then
        sSQL = "INSERT INTO " & sAudTmpTable & " ( audType, audDate, audUser ) " & _
            "SELECT 'EditFrom' AS Expr1, Now() AS Expr2, NetworkUserName() AS Expr3, " & sTable & ".* " & _
            "FROM " & sTable & " WHERE (" & sTable & "." & sKeyField & " = " & lngKeyValue & ");"
        db.Execute sSQL, dbFailOnError
    End If
    AuditEditBegin = True

Exit_AuditEditBegin:
    Set db = Nothing
    Exit Function

Err_AuditEditBegin:
    Call LogError(Err.Number, Err.Description, conMod & ".AuditEditBegin()", , False)
    Resume Exit_AuditEditBegin
End Function


Function AuditEditEnd(sTable As String, sAudTmpTable As String, sAudTable As String, _
    sKeyField As String, lngKeyValue As Long, bWasNewRecord As Boolean) As Boolean
'On Error GoTo Err_AuditEditEnd
    'Purpose:    Write the audit trail to the audit table.
    'Arguments:  sTable = name of table being audited.
    '            sAudTmpTable = name of the temp audit table.
    '            sAudTable = name of the audit table.
    '            sKeyField = name of the AutoNumber field.
    '            lngKeyValue = Value of the AutoNumber field.
    '            bWasNewRecord = True if this was a new insert.
    'Return:     True if successful
    'Usage:      Called in form's AfterUpdate event. Example:
    '                Call AuditEditEnd("tblInvoice", "audTmpInvoice", "audInvoice", "InvoiceID", Me.InvoiceID, bWasNewRecord)
    Dim db As DAO.Database
    Dim sSQL As String
    Set db = DBEngine(0)(0)

    If bWasNewRecord Then
        ' Copy the new values as "Insert".
        sSQL = "INSERT INTO " & sAudTable & " ( audType, audDate, audUser ) " & _
            "SELECT 'Insert' AS Expr1, Now() AS Expr2, NetworkUserName() AS Expr3, " & sTable & ".* " & _
            "FROM " & sTable & " WHERE (" & sTable & "." & sKeyField & " = " & lngKeyValue & ");"
        db.Execute sSQL, dbFailOnError
    Else
        ' Copy the latest edit from temp table as "EditFrom".
        sSQL = "INSERT INTO " & sAudTable & " SELECT TOP 1 " & sAudTmpTable & ".* FROM " & sAudTmpTable & _
            " WHERE (" & sAudTmpTable & ".audType = 'EditFrom') ORDER BY " & sAudTmpTable & ".audDate DESC;"
        db.Execute sSQL
        ' Copy the new values as "EditTo"
        sSQL = "INSERT INTO " & sAudTable & " ( audType, audDate, audUser ) " & _
            "SELECT 'EditTo' AS Expr1, Now() AS Expr2, NetworkUserName() AS Expr3, " & sTable & ".* " & _
            "FROM " & sTable & " WHERE (" & sTable & "." & sKeyField & " = " & lngKeyValue & ");"
        db.Execute sSQL
        ' Empty the temp table.
        sSQL = "DELETE FROM " & sAudTmpTable & ";"
        db.Execute sSQL, dbFailOnError
    End If
    AuditEditEnd = True

Exit_AuditEditEnd:
    Set db = Nothing
    Exit Function

Err_AuditEditEnd:
    Call LogError(Err.Number, Err.Description, conMod & ".AuditEditEnd()", , False)
    Resume Exit_AuditEditEnd
End Function

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This is a cached tutorial, reproduced with permission.

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