Nevertheless Object Oriented Programming may be hard for people accustomed to Procedural Programming because Object Oriented Programming is Non-Linear whereas the old way is Linear or Sequential. So why would you want to complicate things ? Because of the Divide-and-Conquer law. By splitting your code into Objects, you can better maintain each component separately by concern and not mix everything like GUI Interface with your Business Logics.

So in this lesson, I’m going to introduce you VBA Class Module and I am supposing that you know at least a bit of VBA (I will surely write some basic VBA tutorial but since there are already plenties, you can probably find one without my help).

The first thing you should know is that there is a type of module which is a class module. Under MS Access 2007 you just have to click on this Icon’s Submenu:

Once inside, you can create and rename the default class1 module:

Let’s rename it to clsPerson (Best Practice in Naming Convention is to prefix each class name with cls) as we’re going to create some properties for it:

Private Id As Long
Private FirstName As String
Private LastName As String
Private BirthDate As Date

To access these properties, you need to create an object or instance first (as a class is just a template for creating objects) with the new instruction like this:

Set oPerson = New clsPerson

so that you could access an oPerson Property like this (using the Immediate Window which is a kind of VBA console):

Debug.Print oPerson.Id

Oops, something’s wrong:

Why ? Because you set the properties as Private, remember ? So let’s turn them into Public:

Public Id As Long
Public FirstName As String
Public LastName As String
Public BirthDate As Date

This time it works as the Immediate Command Window returns 0 (by default a Long Property will be inialized automatically to zero by default):

That’s fine now isn’t it … except we’ve just defeated one of the purpose of good OOP which is to protect the properties from the external world by controlling their access (like locking your house with a key to forbid people to steal your assets). So go back to private please !

But wait how are we going to access them ? Well, we’re going to create Accessors or Getters and Setters (we’ll see in the future that this also is evil but it is less evil than outright Public Properties and let’s not be too harsh for a beginning). Getters and Setters are like Doors that you must open to access the private properties and are created with Property Let / Property Get:

Private m_lId As Long
Private m_sFirstName As String
Private m_sLastName As String
Private m_dtBirthDate As Date

Public Property Get Id() As Long

    Id = m_lId

End Property

Public Property Let Id(ByVal lId As Long)

    m_lId = lId

End Property

Public Property Get FirstName() As String

    FirstName = m_sFirstName

End Property

Public Property Let FirstName(ByVal sFirstName As String)

    m_sFirstName = sFirstName

End Property

Public Property Get LastName() As String

    LastName = m_sLastName

End Property

Public Property Let LastName(ByVal sLastName As String)

    m_sLastName = sLastName

End Property

Public Property Get BirthDate() As Date

    BirthDate = m_dtBirthDate

End Property

Public Property Let BirthDate(ByVal dtBirthDate As Date)

    m_dtBirthDate = dtBirthDate

End Property

Yawn … All this for just that ? Are you kidding ? Well I know, that seems overkilled but OOP is a Paradigm shift and you need some times to get accustomed to all this. And don’t worry if it’s so verbose, I’ll show you in future lesson how you can use a nice tool to cut off this burden so that even Visual Studio Professional Coders would envy you

Good Practice, see you next !

Of course you can use MS Access Tool to rebuild the link but this is rather tedious so here’s a VBA script to do so automatically:

Public Function RelinkAllAccessTables(SourceDatabaseName )

    Dim DB As DAO.Database
    Dim RS As Recordset

    Set DB = CurrentDb
    SQL = "select name from MsysObjects where type = 6"
    Set RS = DB.OpenRecordset(SQL)
    RS.MoveLast
    Debug.Print RS.RecordCount
    RS.MoveFirst
    i = 0
    Do While Not RS.EOF
        SourceTableName = RS(0)
        Call RelinkLocalTable(SourceTableName, SourceDatabaseName)
        RS.MoveNext
        i = i + 1
        Debug.Print i
    Loop

End Function

The RelinkLocalTable essentially redefine the Tabledef Connect property to the new database path:

Public Function RelinkLocalTable(p_SourceTableName, p_SourceDatabaseName, Optional p_TargetTableName)

    TablePath = CurrentProject.Path & "\"
    SourceDatabaseName = p_SourceDatabaseName

    Dim DB As DAO.Database
    Dim RS As Recordset

    Set DB = CurrentDb()
    Dim tempTableDef As DAO.TableDef

    If IsMissing(p_TargetTableName) Then
        TargetTableName = p_SourceTableName
    Else
        TargetTableName = p_TargetTableName
    End If

    SourceTableName = p_SourceTableName
    SourceDatabaseName = p_SourceDatabaseName

    Set tempTableDef = DB.TableDefs(TargetTableName)
        If tempTableDef.SourceTableName  "" Then
            tempTableDef.Connect = ";DATABASE=" & TablePath & SourceDatabaseName
            tempTableDef.RefreshLink
      End If

End Function

To use the RelinkAllAccessTables function just call for example:

call RelinkAllAccessTables("Northwind.mdb")

For more info see:
Automatic Table Relinking

The VBA function below will query the MsysObjects table to get the list of all tables (type = 1) in the current database:

'call deleteAllTables
Public Function deleteAllTables()

    Dim DB As Database
    Dim RS As Recordset
    Dim Table As String

    Set DB = CurrentDb()
    Set RS = DB.OpenRecordset("Select name from MsysObjects where (type = 1 and name not like 'Msys*')")

    Do While Not RS.EOF
        TableName = RS("Name")
        On Error Resume Next
        DoCmd.DeleteObject acTable, TableName
        RS.MoveNext
    Loop
    RS.Close
    MsgBox ("All Tables have been deleted")
End Function