Efficiently fill resultset in object model

Question

Hi, I have an object model whose structure is
Dashboard
  List of panels
    List of containers
      List of widgets
If i get whole dashboard, with panels + containers + widgets, from Database then multiple I/O requires I want to get it in one I/O .For this i prepared a query which gives me this resultset.

DASHBOARDID   PANELID  CONTAINERID  WIDGETID
13                          11                    5              2
13                          11                    5              3
13                          11                    6              4
13                          11                    6              5
13                          12                    7              6
13                          12                    7              7
13                          12                    8              8
13                          12                    8              9

Using list datastructure this model is able to be filled but it takes time i want to efficiently fill this resultset in above object model. is there nay way ?

Answer 1

If you are not strictly limited to using JDBC, an ORM solution would resolve your issue. E.g. in Hibernate, you can easily configure your entity mapping to use lazy or eager loading. In the latter case, when you load a Dashboard object, the persistence framework fetches all the contained panels, containers and widgets with 1 to 4 queries total (depending on configuration - note that a single join query for 4 tables might not be optimal if there are many rows), and initialize the whole object graph for you automatically.

Answer 2

The strict ordering and nesting in the data makes this fairly straightforward. The solution is a loop that look for changes in ID - when the ID changes a new instance is created. It iteration of the loop maintains the current dashboard, panel, component, widget. For example

Dashboard dashboard,
Panel panel;
Container container;
Widget widget;
List<Dashboard> dashboards; 
ResultSet rs = ...;
while (rs.next())
{
   int dashboardID = rs.getInt(1);
   int panelID = rs.getInt(2);
   int dashboardID = rs.getInt(3);
   int dashboardID = rs.getInt(4);

   if (dashboard==null || dashboardID!=dashboard.id()) {
      dashboard = new Dashboard(dashboardID);
      dashboards.add(dashboard);
   }
   if (panel==null || panelID!=panel.id()) {
      panel = new Panel(panelID);
      dashboard.add(panel);
   }
   if (container!=null || containerID!=container.id()) {
      container = new Container(containerID);
      panel.add(container);
   }
   // wimilarly for widget

}
// all dashboards in "dashboards" initialized with hierarchy