Question

I am dealing with one table on the database. The columns are: id, name, parent_id
(parent_id would be an id on the table. if parent_id is null, the record is a parent.)

What would be the best way to copy and create same record through recursive loop from recursive loop so I can create same tree structure as it is:

• item
  • item1
    • item 1.1
      • item 1.1.1
      • item 1.1.2
    • item 1.2
  • item 2
    • item 2.1
      • item 2.1.1
    • item 2.2
  • item3

etc and it is like nth level.

Answer 1

You don’t need to use recursion, the code will be clearer if you don’t.

First the result set needs to be ordered by id and parent_id, then you just iterate through the result set using a java.util.Map as an index, something like this:

Map<Object, Item> items = new HashMap<Object, Item>(); 

if (resultSet.next()) 
{
  Item root = createItem(resultSet);
  items.put(root.getId(), root);

  while (resultSet.next()) 
  {
    Item item = createItem(resultSet);
    items.put(item.getId(), item);

    Item parent = items.get(item.getParentId()); 
    if (parent != null) 
    {
      parent.addChild(item);
    }
    else
    {
      ...
    }
  }

  return root;
}
else 
{
  ...
}