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1-Should we upgrade to VB .NET:
The migration to VB .Net is not an obligation, and an application that works perfectly today and meets your needs no reasons to migrate to VB .Net. Nevertheless, it may be an update or new version of your project requires you to choose between Visual Basic and Visual Basic .Net. This choice can not be done by considering several factors and assessing their advantages and disadvantages. Once the decision, we must define the strategy to achieve the migration.

1.1-benefits:
The major new VB .Net:
• Visual Basic .NET is a true object-oriented language (inheritance, polymorphism is a reality).
• Error handling is improved through structured exception handling.
• The management of multi applications is now possible.
The .NET platform:
• Improved scalability: The ADO .Net improve the scalability of your application by promoting offline and reducing the number of connections and DBMS locks. ASP Session management has been improved and can be shared among several servers in a Web farm.
• Increased performance: The Data Reader object was designed for speed of data access. ASP .Net pages are now compiled.
• Easier deployment: The deployment of your application will be made by a simple XCOPY.

2. What strategy to achieve the migration?

Three migration options are available, either completely rewrite your application in Visual Basic .NET, or migrate it totally or partially to migrate.

2.1. Rewriting your application

This option is useful if you want:
• Benefit from improved performance and increased scalability of your application (ASP .Net ADO .Net to use and helps improve)
• Migrate your application but the existing Visual Basic code does not have an equivalent in Visual Basic .NET or it is impossible to migrate.
This solution has the following disadvantages:
• No existing code reusability
• important human and financial investment

2.2. The total migration:

Advantage:
• Reuse of part of the existing code.
• Improved performance and scalability for the parties migrated.
Disadvantages:
• The migrated code may not be effective and will require adjustments.
• Some portions migrated (eg using ADO) does not benefit from the advantages of .NET
The Migrating a Visual Basic project to VB .Net
The project we're studying is an n-tier project respecting the Windows DNA architecture. It consists of an introduction to ASP layer, a layer of business objects that implement business rules and a data persistence layer using ADO. We will migrate a part of the latter layer.

1-General Considerations

1.1. Unsupported features

Some features are not supported by VB .NET and can not be migrated by the wizard:
• The OLE Container control.
• Dynamic Data Exchange (DDE).
• The DAO and RDO data Binding.
• Visual Basic controls 5.
• DHTML applications.
• The Active X Documents.
• The property pages.
Applications using these features should be left unchanged in Visual Basic 6.0 (Property pages for example) or migrating to .NET (processing documents ActiveX controls users).

1.2. Unsupported keywords

Some keywords have been removed from language.
Keyword Description

Def <type> must explicitly declare variables.
Goto / Gosub These instructions can be replaced with If or Select Case.
Gosub / Return These instructions can be replaced by the use of functions or procedures.
Option Base 0 | 1 The tables are indexed at 0.
VarPtr, ObjPtr, StrPtr These functions used to retrieve the memory address some variables are no longer used.
LSet This function allows the assignment data type is no longer

2. The upgrade strategy

It is recommended that you install your project on the machine which will be launched migration. This guarantees that the VB6 project works and that all the elements used by the project (components, controls ...) are available at the time of migration.
Moreover the migration wizard only accepts projects Visual Basic 6. So if you have earlier versions, it is recommended to migrate prior to Visual Basic 6.

Public Class DataAccess

Inherits System.EnterpriseServices.ServicedComponent

        Private sConstructString As String

        Private Const NomModule As String = "DataClient"

        Protected Overrides Sub Construct(ByVal constructString As String)

            sConstructString = constructString

        End Sub 'Construct    

'UPGRADE_ISSUE: La constante vbLogToNT n'a pas été mise à niveau. 

'Cliquez ici : 'ms-help://MS.VSCC.2003/commoner/redir/redirect.htm?keyword="vbup2070"'

'UPGRADE_ISSUE: App méthode App.StartLogging - Mise à niveau non effectuée 

'Cliquez ici : 'ms-help://MS.VSCC.2003/commoner/redir/redirect.htm?keyword="vbup2069"'

App.StartLogging("", vbLogToNT)

'UPGRADE_ISSUE: La constante vbLogEventTypeError n'a pas été mise à niveau. 

'Cliquez ici : 'ms-help://MS.VSCC.2003/commoner/redir/redirect.htm?keyword="vbup2070"'

'UPGRADE_ISSUE: App méthode App.LogEvent - Mise à niveau non effectuée 

'Cliquez ici : 'ms-help://MS.VSCC.2003/commoner/redir/redirect.htm?keyword="vbup2069"'

App.LogEvent(Err.Source & " " & Err.Description, vbLogEventTypeError)

The manually migrated code becomes:

Imports System.Diagnostics.EventLog
'...
Dim myLog As New EventLog("Application", System.Environment.MachineName, "Classe DataAccess")
myLog.WriteEntry(Err.Source & " " & Err.Description, EventLogEntryType.Error)
                    

Transaction management
Our class is transactional and we must preserve this property. 
To do this is to use the mechanisms of declarative transactions proposed by
 the System.EnterprisesServices ( ServiceComponents) class namespace.

On the one hand we will define in class header attribute "TransactionAttribute" to define
the transactional properties of the class. 
Furthermore we will use the attribute "AutoComplete" about each method to automatically 
in the SetComplete method on success of the transaction is SetAbort on error.



Here's the code before and after migration:

Function CreerClient(…)


Dim ctx As ObjectContext       
'...
        Set ctx = GetObjectContext
        If Not ctx Is Nothing Then
       ctx.SetComplete
       Set ctx = Nothing
        End If
Imports System.EnterpriseServices
        
<Transaction(TransactionOption.Required)> _
        Public Class DataAccess
    Inherits System.EnterpriseServices.ServicedComponent
                                                     
        <AutoComplete()> Function CreerClient(ByVal sSiret As String, ByVal sNomClient As String, _
               ByVal iNumero As Short, _
               ByVal sRue As String, _
               ByVal sCodePostal As String, _
               ByVal sCommune As String, _
               ByRef vIdentifiant As Object) As Short



Migration is now complete (see Comparison migrated codes),
 it remains only perform regression
 tests. 
We could continue incorporating new .NET functionality 
(replacing COM components in .NET components, ADO, ADO .Net passage, change in the error
 handling ...).








final result :

Vb6 Code:


Option Explicit

Private Const NomModule = "DataClient"
                     
Function CreerClient(ByVal sSiret As String, _
        ByVal sNomClient As String, _
        ByVal iNumero As Integer, _
        ByVal sRue As String, _
        ByVal sCodePostal As String, _
        ByVal sCommune As String, _
        ByRef vIdentifiant As Variant) As Integer
                    
        On Error GoTo GestionErreur
                              
        Dim oConnexion As ADODB.Connection
        Dim oRecordset As ADODB.Recordset
        Dim oCommand As ADODB.Command
        Dim ctx As ObjectContext
         
        Dim iCodeRetour As Integer 'contient le code retour de la proc stock
                                
        Set oCommand = New ADODB.Command
                               
        With oCommand
               .Parameters.Append .CreateParameter("@Retour", adInteger, _
               adParamReturnValue)
               '...
        End With
                                 
        Set oConnexion = New ADODB.Connection
        oConnexion.Open sConstructString
                               
        oConnexion.BeginTrans
        With oCommand
                .CommandType = adCmdStoredProc
                .CommandText = "Insert_Client"
                Set .ActiveConnection = oConnexion
        End With
                               
        oCommand.Execute , , adExecuteNoRecords
                               
        'recuperation du code retour de la procédure stockée
        vIdentifiant = oCommand.Parameters("@Retour").Value
                                 
        Set ctx = GetObjectContext
        If Not ctx Is Nothing Then
           ctx.SetComplete
           Set ctx = Nothing
        End If
                       




Code vb.net:           




Option Strict Off
Option Explicit On 
Imports System.Diagnostics.EventLog
Imports System.EnterpriseServices
                       
<Transaction(TransactionOption.Required)> _
Public Class DataAccess
Inherits System.EnterpriseServices.ServicedComponent
        Private Const NomModule As String = "DataClient"
                       
        <AutoComplete()> _ 
        Function CreerClient(ByVal sSiret As String, ByVal sNomClient As String,  _ 
               ByVal iNumero As Short, ByVal sRue As String, ByVal sCodePostal As String, _
               ByVal sCommune As String, ByRef vIdentifiant As Object) As Short
               On Error GoTo GestionErreur
                                              
               Dim oConnexion As ADODB.Connection
               Dim oRecordset As ADODB.Recordset
               Dim oCommand As ADODB.Command
                     
               Dim iCodeRetour As Short 
              
               
               oCommand = New ADODB.Command
               
               With oCommand
                    .Parameters.Append(.CreateParameter("@Retour",  _ 
                            ADODB.DataTypeEnum.adInteger, _ 
                            ADODB.ParameterDirectionEnum.adParamReturnValue))
                        '...
            End With
                       
               oConnexion = New ADODB.Connection
               oConnexion.Open(sConstructString)
               
               With oCommand
                    .CommandType = ADODB.CommandTypeEnum.adCmdStoredProc
                    .CommandText = "Insert_Client"
                    .ActiveConnection = oConnexion
               End With
               
                   oCommand.Execute(, , ADODB.ExecuteOptionEnum.adExecuteNoRecords)
                       
                   vIdentifiant = oCommand.Parameters("@Retour").Value
                       
                   If (Not oRecordset Is Nothing) Then
                      If oRecordset.State = ADODB.ObjectStateEnum.adStateOpen Then _ 
                         oRecordset.Close()
                      End If
                       
                   If (Not oConnexion Is Nothing) Then
                      If oConnexion.State = ADODB.ObjectStateEnum.adStateOpen Then  _
                         oConnexion.Close()
                      End If
                   End If