Private Shared Sub ConstraintCollectionChanged()
        ' Demonstrate ConstraintCollection.CollectionChanged event.
        Try
            ' Create Customers table.
            Dim customersTable As New DataTable("Customers")
            customersTable.Columns.Add("id", Type.GetType("System.Int32"))
            customersTable.Columns.Add("Name", Type.GetType("System.String"))
            AddHandler customersTable.Constraints.CollectionChanged, _ 
                New System.ComponentModel.CollectionChangeEventHandler( _
                AddressOf Collection_Changed)

            ' Create Orders table.
            Dim ordersTable As New DataTable("Orders")
            ordersTable.Columns.Add("CustID", Type.GetType("System.Int32"))
            ordersTable.Columns.Add("CustName", Type.GetType("System.String"))
            AddHandler ordersTable.Constraints.CollectionChanged, _
                New System.ComponentModel.CollectionChangeEventHandler( _
                AddressOf Collection_Changed)

            ' Create unique constraint.
            Dim constraint As New UniqueConstraint(customersTable.Columns("id"))
            customersTable.Constraints.Add(constraint)

            ' Create unique constraint and specify as primary key.
            ordersTable.Constraints.Add( _
                "pKey", ordersTable.Columns("CustID"), True)

            ' Remove constraints.
            customersTable.Constraints.RemoveAt(0)

            ' Results in an Exception. You can't remove 
            ' a primary key constraint.
            ordersTable.Constraints.RemoveAt(0) 
 
        Catch ex As Exception
            ' Process exception and return.
            Console.WriteLine($"Exception of type {ex.GetType()} occurred.")
    End Try
End Sub

    Private Shared Sub Collection_Changed(sender As object, _
        ex As System.ComponentModel.CollectionChangeEventArgs)
        Console.WriteLine($"List_Changed Event: '{ex.Action}'{vbTab} element={ex.Element}")
    End Sub