Public Class AdventureWorksProxy
    ' Define the object context to be provided. 
    Private contextProxy As New AdventureWorksEntities()

    Public Sub New()
        ' When the object is initialized, register the 
        ' handler for the SavingChanges event. 
        AddHandler contextProxy.SavingChanges, AddressOf context_SavingChanges
    End Sub

    ' Method that provides an object context. 
    Public ReadOnly Property Context() As AdventureWorksEntities
        Get
            Return contextProxy
        End Get
    End Property

    ' SavingChanges event handler. 
    Private Sub context_SavingChanges(ByVal sender As Object, ByVal e As EventArgs)
        ' Ensure that we are passed an ObjectContext 
        Dim context As ObjectContext = TryCast(sender, ObjectContext)
        If context IsNot Nothing Then

            ' Validate the state of each entity in the context 
            ' before SaveChanges can succeed. 
            For Each entry As ObjectStateEntry In context.ObjectStateManager.GetObjectStateEntries(EntityState.Added Or EntityState.Modified)
                ' Find an object state entry for a SalesOrderHeader object. 
                If Not entry.IsRelationship AndAlso (entry.Entity.GetType() Is GetType(SalesOrderHeader)) Then
                    Dim orderToCheck As SalesOrderHeader = TryCast(entry.Entity, SalesOrderHeader)

                    ' Call a helper method that performs string checking 
                    ' on the Comment property. 
                    Dim textNotAllowed As String = Validator.CheckStringForLanguage(orderToCheck.Comment)

                    ' If the validation method returns a problem string, raise an error. 
                    If textNotAllowed <> String.Empty Then
                        Throw New ArgumentException(String.Format("Changes cannot be " & _
                                                                    "saved because the {0} '{1}' object contains a " & _
                                                                    "string that is not allowed in the property '{2}'.", _
                                                                    entry.State, "SalesOrderHeader", "Comment"))
                    End If
                End If
            Next
        End If
    End Sub
End Class