private async void OnRebuildDatabase(object sender, RoutedEventArgs e)
{
var path = Windows.Storage.ApplicationData.Current.LocalFolder.Path;
System.Diagnostics.Debug.WriteLine($"INFO: local files are in {path}");
var bookdb = BookDataContext.Get();
int nbook = await RdfReader.ReadDirAsync(bookdb);
if (nbook < 5)
{
App.Error($"Error when rebuilding database; only got {nbook} for {path}");
}
// Will clear out the old db and save as needed.
}