The example creates a duplicate Dynaset from the recordset of a data control, and then in the Validate event, searches for a duplicate record in the cloned Dynaset in order to validate the entry when a user is attempting to add a new record.
' Declarations section.
Dim MyDup As Dynaset
...
Sub Form_Load ()
Data1.DatabaseName = "BIBLIO.MDB" ' Set data properties.
Data1.RecordSource = "Authors"
Data1.Refresh ' Open database.
Set MyDup = Data1.Recordset.Clone() ' Clone recordset.
...
Sub Data1_Validate ()
' Make sure a change has taken place.
If Not Text1.DataChanged Then Exit Sub
' In the cloned recordset, find a matching record.
MyDup.Find "Author = " & Text1.Text
If Not MyDup.NoMatch Then ' If a match is found...
...