IndexNulls Property Example (VB)

IndexNulls Property Example (VB)

This example demonstrates the IndexNulls property of an Index. The code creates a new index and sets the value of IndexNulls based on user input (from a list box named List1). Then, the Index is appended to the Employees Table in the Northwind Catalog. The new Index is applied to a Recordset based on the Employees table, and the Recordset is opened. A new record is added to the Employees table, with a Null value in the indexed field. Whether this new record is displayed depends on the setting of the IndexNulls property.

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