Get a dataframe of metrics from this storage

def get_frame(self):
        """ Get a dataframe of metrics from this storage """
        metric_items = list(self.db.metrics.find({'run_name': self.model_config.run_name}).sort('epoch_idx'))
        if len(metric_items) == 0:
            return pd.DataFrame(columns=['run_name'])
        else:
            return pd.DataFrame(metric_items).drop(['_id', 'model_name'], axis=1).set_index('epoch_idx')