Public Class SchnellGeschriebenerDAL
    Public Property ConnectionString() As String
 
    Public Sub New(ByVal connectionString)
        Me.ConnectionString = connectionString
    End Sub
 
    Public Function Exists() As Boolean
        Dim con As OleDbConnection = Nothing
        Try
            con = New OleDbConnection(ConnectionString)
            con.Open()
            Return True
        Catch ex As Exception
        Finally
            If (con IsNot Nothing) Then
                con.Close()
            End If
        End Try
        Return False
    End Function
 
    Public Sub ChangeDBFileName(ByVal fileName As String)
        Dim cb As New OleDbConnectionStringBuilder(ConnectionString)
        cb.DataSource = fileName
        ConnectionString = cb.ToString()
    End Sub
 
    Public Function ReadDataTable(ByVal dt As DataTable, ByVal sql As String, _
      ByVal parameter As Dictionary(Of String, Object)) As DataTable
        Using adap As New OleDbDataAdapter(sql, ConnectionString)
            For Each kv In parameter
                adap.SelectCommand.Parameters.AddWithValue(kv.Key, kv.Value)
            Next
            If (dt Is Nothing) Then
                dt = New DataTable()
            End If
            adap.Fill(dt)
        End Using
 
        Return dt
    End Function
    Public Function ReadDataTable(ByVal tableName As String) As DataTable
        Return ReadDataTable(Nothing, String.Format("SELECT * FROM {0}", _
          tableName), Nothing)
    End Function
 
    Public Function WriteDataTable(ByVal dt As DataTable, ByVal tablename As _
      String) As Integer
 
        Using adap As New OleDbDataAdapter(String.Format("SELECT * FROM {0}", _
          tablename), ConnectionString)
            Dim cb As New OleDbCommandBuilder(adap)
            Return adap.Update(dt)
        End Using
    End Function
 
End Class
 
 
Public Class KundenlistRepository
 
    Protected dal As SchnellGeschriebenerDAL
 
    Public Sub New(ByVal connectionstring As String)
        dal = New SchnellGeschriebenerDAL(connectionstring)
    End Sub
 
    Public Function ReadAll() As DataTable
        Return dal.ReadDataTable("KundenListe")
    End Function
 
    Public Function ReadByID(ByVal id As Integer) As DataTable
        Dim param As New Dictionary(Of String, Object)
        param.Add("@ID", id)
        Return dal.ReadDataTable(Nothing, "SELECT * FROM KundenListe WHERE" & _
          "ID=?", param)
    End Function
 
    Public Function Save(ByVal dt As DataTable) As Integer
        Return dal.WriteDataTable(dt, "KundenListe")
    End Function
End Class
 
 
Public Class KundenListForm
    Inherits System.Windows.Forms.Form
 
    Private klRepository As KundenlistRepository
    Private kundenDataTable As DataTable
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        klRepository = New KundenlistRepository(My.Settings.datenbank)
    End Sub
 
    Private Sub LoadAllButton_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles LoadAllButton.Click
        kundenDataTable = klRepository.ReadAll()
        gridKD.DataSource = kundenDataTable
    End Sub
End Class