Ejemplo de propiedad IndexNulls (VB)

En este ejemplo se muestra la propiedad IndexNulls de un objeto Index. El código crea un nuevo índice y establece el valor de IndexNulls en función de la entrada del usuario (de un cuadro de lista denominado List1). A continuación, el índice se anexa a la tabla Employees del catálogo Northwind. El nuevo índice se aplica a un objeto Recordset basado en la tabla Employees y se abre el objeto Recordset. Se agrega un nuevo registro a la tabla Employees, con un valor Null en el campo indizado. Si se muestra este nuevo registro depende del valor de la propiedad IndexNulls.

' BeginIndexNullsVB  
Private Sub cmdIndexNulls_Click()  
    IndexNullsX  
End Sub  
  
Sub IndexNullsX()  
  
    Dim cnn As New ADODB.Connection  
    Dim catNorthwind As New ADOX.Catalog  
    Dim idxNew As New ADOX.Index  
    Dim rstEmployees As New ADODB.Recordset  
    Dim varBookmark As Variant  
  
    ' Connect the catalog.  
    cnn.Open "Provider=Microsoft.Jet.OLEDB.4.0;" & _  
        "data source=c:\Program Files\" & _  
        "Microsoft Office\Office\Samples\Northwind.mdb;"  
  
    Set catNorthwind.ActiveConnection = cnn  
  
    ' Append Country column to new index  
    idxNew.Columns.Append "Country"  
    idxNew.Name = "NewIndex"  
  
    ' Set IndexNulls based on user selection in listbox List1  
    Select Case List1.List(List1.ListIndex)  
        Case "Allow"  
            idxNew.IndexNulls = adIndexNullsAllow  
        Case "Ignore"  
            idxNew.IndexNulls = adIndexNullsIgnore  
        Case Else  
            End  
    End Select  
  
    'Append new index to Employees table  
    catNorthwind.Tables("Employees").Indexes.Append idxNew  
  
    rstEmployees.Index = idxNew.Name  
    rstEmployees.Open "Employees", cnn, adOpenKeyset, _  
        adLockOptimistic, adCmdTableDirect  
  
    With rstEmployees  
        ' Add a new record to the Employees table.  
        .AddNew  
        !FirstName = "Gary"  
        !LastName = "Haarsager"  
        .Update  
  
        ' Bookmark the newly added record  
        varBookmark = .Bookmark  
  
        ' Use the new index to set the order of the records.  
        .MoveFirst  
  
        Debug.Print "Index = " & .Index & _  
            ", IndexNulls = " & idxNew.IndexNulls  
        Debug.Print "  Country - Name"  
  
        ' Enumerate the Recordset. The value of the  
        ' IndexNulls property will determine if the newly  
        ' added record appears in the output.  
        Do While Not .EOF  
            Debug.Print "    " & _  
                IIf(IsNull(!Country), "[Null]", !Country) & _  
                " - " & !FirstName & " " & !LastName  
            .MoveNext  
        Loop  
  
        ' Delete new record because this is a demonstration.  
        .Bookmark = varBookmark  
        .Delete  
  
        .Close  
    End With  
  
    ' Delete new Index because this is a demonstration.  
    catNorthwind.Tables("Employees").Indexes.Delete idxNew.Name  
    Set catNorthwind = Nothing  
  
End Sub  
' EndIndexNullsVB  

Consulte también

Objeto Index (ADOX)
IndexNulls (propiedad, ADOX)