Is Splitting a Dataset needed for a ColumnWithNativeLazyDrilldown chart?

Flow
1

Hi guys,

Currently, I have a SQL result dataset that consists of data columns of Branch, Cashier, Transaction Count, Total Sales. The data is grouped according Branch, then by Cashier.

I would want to add a ColumnWithNativeLazyDrilldown chart in one of my app’s views with first level by Branch and the second level would be the cashiers of a branch selected. Having read the sample code [here]
(https://demo.vaadin.com/charts/#ColumnWithNativeLazyDrilldown), there are a few questions if using a ResultSet.

  1. Does the dataset needs to be break into two to cater for the drilldown ?
for(int i=0; i<objList.size(); i++){
                SalesByCashierMetric sm = objList.get(i);
                DataSeriesItem item = new DataSeriesItem(sm.getsOutlet(),sm.getdTotalSales());
                item.setId(""+i);
                series.addItemWithDrilldown(item);
                //DataSeries subSeries = 
                //series.add(new DataSeriesItem(sm.getsOutlet(),sm.getdTotalSales()));
                
                chart.getConfiguration().getxAxis().addCategory(sm.getsOutlet());
            }
  1. Is it correct that drilldowns are usually done in two or loops as in the first one shown above in main level, the second level in form of another loop?

Thanks in advance
Melvin