Private Sub CreateUniqueConstraint(ByVal dataSetSuppliers As DataSet)
    Dim uniqueConstraint As UniqueConstraint

    ' Get the DataColumn of a table in a DataSet.
    Dim dataColumn As DataColumn
    dataColumn = dataSetSuppliers.Tables("Suppliers").Columns("SupplierID")

    ' Create the constraint.
    uniqueConstraint = New UniqueConstraint("supplierIdConstraint", dataColumn)

    ' Add the constraint to the ConstraintCollection of the DataTable.
    dataSetSuppliers.Tables("Suppliers").Constraints.Add(uniqueConstraint)
End Sub

Private Sub MakeTableWithUniqueConstraint()
    ' Create a DataTable with 2 DataColumns.
    Dim dataTable As New DataTable("dataTable")
    Dim idColumn As New DataColumn( _
        "ID", System.Type.GetType("System.Int32"))
    Dim nameColumn As New DataColumn( _
        "Name", System.Type.GetType("System.String"))
    dataTable.Columns.Add(idColumn)
    dataTable.Columns.Add(nameColumn)

    ' Run procedure to create a constraint.
    AddUniqueConstraint(dataTable)

    ' Add one row to the table.
    Dim dataRow As DataRow
    dataRow = dataTable.NewRow()
    dataRow("ID") = 1
    dataRow("Name") = "John"
    dataTable.Rows.Add(dataRow)

    ' Display the constraint name.
    Console.WriteLine(dataTable.Constraints(0).ConstraintName)

    ' Try to add an identical row,
    ' which throws an exception.
    Try
        dataRow = dataTable.NewRow()
        dataRow("ID") = 1
        dataRow("Name") = "John"
        dataTable.Rows.Add(dataRow)
    Catch ex As Exception
        Console.WriteLine("Exception Type: {0}", ex.GetType())
        Console.WriteLine("Exception Message: {0}", ex.Message)
    End Try
End Sub

Private Sub AddUniqueConstraint(ByVal dataTable As DataTable)
    ' Create the DataColumn array.
    Dim dataColumns(1) As DataColumn
    dataColumns(0) = dataTable.Columns("ID")
    dataColumns(1) = dataTable.Columns("Name")

    ' Create the constraint on both columns.
    Dim uniqueConstraint As UniqueConstraint = _
        New UniqueConstraint("idNameConstraint", dataColumns)
    dataTable.Constraints.Add(uniqueConstraint)
End Sub