ServerSide Timestamping in the Audit Trail System(XAF时间戳在审核中的应用)

By default, the Audit Trail system uses the client time stamping. When an Audit Data Item is saved to the data storage, the ModifyOn property is initialized with the time of the computer which has been used to perform the change. It causes information inauthenticity, because two changes made at the same time can be saved as if they were made at different moments (for example, if these computers are in the different time zones). To avoid this effect, you should use server-side time stamping. To do this, you need to replace the default Local Audit Timestamp Strategy with a server side time stamp strategy. This topic demonstrates how to implement a custom Audit Timestamp Strategy, and set it for the Audit Trail system.

To implement an Audit Timestamp Strategy, you should implement the IAuditTimestampStrategy interface. Further on, you'll see how to implement a Timestamp Web Service and MSSql Server Timestamp Strategy.

Show Me

The complete sample project is available in the DevExpress Code Central database at http://www.devexpress.com/example=E1808. Depending on the target platform type (ASP.NET, WinForms, etc), you can either run this example online or download an auto-executable sample.

Timestamp Web Service

• Add an Asp.NET Web Service to your solution.
  
• Add the GetTime method to the new service's implementation:

  C#

  VB

  [WebService(Namespace = "http://localhost/TimestampService/")]
  [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
  public class TimestampWebService : System.Web.Services.WebService {
     [WebMethod]
     public DateTime GetTime() {
        return DateTime.Now;
     }
  }
  

  <WebService(Namespace:="http://localhost/TimestampService/"), _
     WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
  Public Class TimestampWebService
     Inherits System.Web.Services.WebService
     <WebMethod()> _
     Public Function GetTime() As DateTime
        Return DateTime.Now
     End Function 
  End Class 
  

  C#	[WebService(Namespace = "http://localhost/TimestampService/")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] public class TimestampWebService : System.Web.Services.WebService { [WebMethod] public DateTime GetTime() { return DateTime.Now; } }
  VB	<WebService(Namespace:="http://localhost/TimestampService/"), _ WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _ Public Class TimestampWebService Inherits System.Web.Services.WebService <WebMethod()> _ Public Function GetTime() As DateTime Return DateTime.Now End Function End Class

• For the WebService attribute, specify the required URL (see the code above).
• Set a Web reference to the new Web Service project to the application module.
• In the application module, implement a WebServiceTimestampStrategy class. It's demonstrated in the following code:

  C#

  VB

  using System;
  using AuditServerSideTimestampingDemo.Module.TimestampService;
  using DevExpress.Persistent.AuditTrail;
  using DevExpress.Xpo;
  namespace MySolution.Module {
     public class WebServiceTimestampStrategy : IAuditTimestampStrategy {
        DateTime cachedTimestamp;
        #region IAuditTimestampStrategy Members
        public DateTime GetTimestamp(AuditDataItem auditDataItem) {
           return cachedTimestamp;
        }
        public void OnBeginSaveTransaction(Session session) {
           try {
              TimestampWebService service = new TimestampWebService();
              cachedTimestamp = service.GetTime();
           }
           catch {
              throw new Exception(
                 "The TimestampWebService cannot be accessed. Make sure that it is running.");
           }
        }
        #endregion
     }
  }
  

  Imports System
  Imports AuditServerSideTimestampingDemo.Module.TimestampService
  Imports DevExpress.Persistent.AuditTrail
  Imports DevExpress.Xpo
  Namespace MySolution.Module 
     Public Class WebServiceTimestampStrategy
        Implements IAuditTimestampStrategy
        Private cachedTimestamp As DateTime
  #Region "IAuditTimestampStrategy Members" 
        Public Function GetTimestamp(ByVal auditDataItem As AuditDataItem) As DateTime _
              Implements IAuditTimestampStrategy.GetTimestamp
           Return cachedTimestamp
        End Function 
        Public Sub OnBeginSaveTransaction(ByVal session As Session) _
              Implements IAuditTimestampStrategy.OnBeginSaveTransaction
           Try 
              Dim service As TimestampWebService = New TimestampWebService()
              cachedTimestamp = service.GetTime()
           Catch 
              Throw New Exception( _
                  "The TimestampWebService cannot be accessed. Make sure that it is running.")
           End Try 
        End Sub 
  #EndRegion
     End Class 
  End Namespace 
  

  C#

  using System; using AuditServerSideTimestampingDemo.Module.TimestampService; using DevExpress.Persistent.AuditTrail; using DevExpress.Xpo; namespace MySolution.Module { public class WebServiceTimestampStrategy : IAuditTimestampStrategy { DateTime cachedTimestamp; #region IAuditTimestampStrategy Members public DateTime GetTimestamp(AuditDataItem auditDataItem) { return cachedTimestamp; } public void OnBeginSaveTransaction(Session session) { try { TimestampWebService service = new TimestampWebService(); cachedTimestamp = service.GetTime(); } catch { throw new Exception( "The TimestampWebService cannot be accessed. Make sure that it is running."); } } #endregion } }

  VB

  Imports System Imports AuditServerSideTimestampingDemo.Module.TimestampService Imports DevExpress.Persistent.AuditTrail Imports DevExpress.Xpo Namespace MySolution.Module Public Class WebServiceTimestampStrategy Implements IAuditTimestampStrategy Private cachedTimestamp As DateTime #Region "IAuditTimestampStrategy Members" Public Function GetTimestamp(ByVal auditDataItem As AuditDataItem) As DateTime _ Implements IAuditTimestampStrategy.GetTimestamp Return cachedTimestamp End Function Public Sub OnBeginSaveTransaction(ByVal session As Session) _ Implements IAuditTimestampStrategy.OnBeginSaveTransaction Try Dim service As TimestampWebService = New TimestampWebService() cachedTimestamp = service.GetTime() Catch Throw New Exception( _ "The TimestampWebService cannot be accessed. Make sure that it is running.") End Try End Sub #EndRegion End Class End Namespace

• Create an instance of the WebServiceTimestampStrategy class and assign it to the AuditTrailService.Instance.TimestampStrategy property. In the code below, this is performed for the Windows Forms application. Actually, you can do it for the ASP.NET application as well.

  C#

  VB

  static void Main() {
     MySolutionWindowsFormsApplication application = new MySolutionWindowsFormsApplication();
     //... 
     IAuditTimestampStrategy timeStampStrategy = new WebServiceTimestampStrategy();
     AuditTrailService.Instance.TimestampStrategy = timeStampStrategy;
     application.Setup();
     //... 
  }
  

  Shared Sub Main()
     Dim _application As MySolutionWindowsFormsApplication = New MySolutionWindowsFormsApplication()
     '... 
     Dim timeStampStrategy As IAuditTimestampStrategy = New WebServiceTimestampStrategy()
     AuditTrailService.Instance.TimestampStrategy = timeStampStrategy
     _application.Setup()
     '... 
  End Sub 
  

  C#	static void Main() { MySolutionWindowsFormsApplication application = new MySolutionWindowsFormsApplication(); //... IAuditTimestampStrategy timeStampStrategy = new WebServiceTimestampStrategy(); AuditTrailService.Instance.TimestampStrategy = timeStampStrategy; application.Setup(); //... }
  VB	Shared Sub Main() Dim _application As MySolutionWindowsFormsApplication = New MySolutionWindowsFormsApplication() '... Dim timeStampStrategy As IAuditTimestampStrategy = New WebServiceTimestampStrategy() AuditTrailService.Instance.TimestampStrategy = timeStampStrategy _application.Setup() '... End Sub

• Run the application. Check that the implemented code works.

MSSql Server Timestamp Strategy

To get the time, you can use the MSSql server. For this purpose, use the Session.Connection property that returns the System.Data.IDbConnection which is associated with the session, and cast it by the SqlConnection type. To get time on the MSSql server, use the GETDATE() function. The following code demonstrates the entire MSSqlServerTimestampStrategy class implementation:

C#

VB

using System;
using System.Data.SqlClient;
using DevExpress.Xpo;
using DevExpress.Persistent.AuditTrail;
namespace MySolution.Module {
   public class MSSqlServerTimestampStrategy : IAuditTimestampStrategy{
      DateTime cachedTimestamp;
      #region IAuditTimestampStrategy Members
      public DateTime GetTimestamp(AuditDataItem auditDataItem) {
         return cachedTimestamp;
      }
      public void OnBeginSaveTransaction(Session session) {
         SqlCommand command = new SqlCommand("select getdate()", (SqlConnection)session.Connection);
         cachedTimestamp = (DateTime)command.ExecuteScalar();
      }
      #endregion
   }
}

Imports System
Imports System.Data.SqlClient
Imports DevExpress.Xpo
Imports DevExpress.Persistent.AuditTrail
Namespace MySolution.Module 
   Public Class MSSqlServerTimestampStrategy
      Implements IAuditTimestampStrategy
      Private cachedTimestamp As DateTime
#Region "IAuditTimestampStrategy Members" 
      Public Function GetTimestamp(ByVal auditDataItem As AuditDataItem) As DateTime _
            Implements IAuditTimestampStrategy.GetTimestamp
         Return cachedTimestamp
      End Function 
      Public Sub OnBeginSaveTransaction(ByVal session As Session) _
            Implements IAuditTimestampStrategy.OnBeginSaveTransaction
         Dim command As SqlCommand = New SqlCommand("select getdate()", _
            CType(session.Connection, SqlConnection))
         cachedTimestamp = CDate(command.ExecuteScalar())
      End Sub 
#EndRegion
   End Class 
End Namespace 

C#

using System; using System.Data.SqlClient; using DevExpress.Xpo; using DevExpress.Persistent.AuditTrail; namespace MySolution.Module { public class MSSqlServerTimestampStrategy : IAuditTimestampStrategy{ DateTime cachedTimestamp; #region IAuditTimestampStrategy Members public DateTime GetTimestamp(AuditDataItem auditDataItem) { return cachedTimestamp; } public void OnBeginSaveTransaction(Session session) { SqlCommand command = new SqlCommand("select getdate()", (SqlConnection)session.Connection); cachedTimestamp = (DateTime)command.ExecuteScalar(); } #endregion } }

VB

Imports System Imports System.Data.SqlClient Imports DevExpress.Xpo Imports DevExpress.Persistent.AuditTrail Namespace MySolution.Module Public Class MSSqlServerTimestampStrategy Implements IAuditTimestampStrategy Private cachedTimestamp As DateTime #Region "IAuditTimestampStrategy Members" Public Function GetTimestamp(ByVal auditDataItem As AuditDataItem) As DateTime _ Implements IAuditTimestampStrategy.GetTimestamp Return cachedTimestamp End Function Public Sub OnBeginSaveTransaction(ByVal session As Session) _ Implements IAuditTimestampStrategy.OnBeginSaveTransaction Dim command As SqlCommand = New SqlCommand("select getdate()", _ CType(session.Connection, SqlConnection)) cachedTimestamp = CDate(command.ExecuteScalar()) End Sub #EndRegion End Class End Namespace

Create an instance of the MSSqlServerTimestampStrategy class and assign it to the AuditTrailService.Instance.TimestampStrategy property. It was demonstrated above for the WebServiceTimestampStrategy class.