protected function onSetAttribute($name, $value) {
    // Listen to these attributes
    $listen = [
      'message_type'=> 'type',
      'message_id'  => 'id',
      'credits_cost'=> 'credits',
      'rb_cost'     => 'cost',
    ];
    // If set
    if (isset($listen[$name])) {
      // If not yet set
      if ( ! isset($this->{$listen[$name]})) {
        // Set corresponding attribute
        $this->{$listen[$name]} = $value;
      }
    }
  }