dá sa nejako zjednodušiť zápis:

            attachmentsListBox.ItemsSource = new ObservableCollection<Attachments>();
            var attachments =
                from attachment in DocumentDB.Attachments
                where attachment.DocumentId == Documents.Id
                select attachment;
            foreach (var attachment in attachments)
                ((ObservableCollection<Attachments>)attachmentsListBox.ItemsSource).Add(attachment);

aby som tam nemal ten zbytočný cyklus? potreboval by som aby mi linq dotaz vracal namiesto výsledkov typu IEnumerable kolekciu typu ObservableCollection.