Question

I have this table:

+-------------------------------+
| NodeID | Parent | HasChildren |
+-------------------------------+
|1000000 |-1      |-1           |
+--------+--------+-------------+
|2409999 |1000000 |-1           |
+-------------------------------+
|2510921 |1000000 |-1           |
+-------------------------------+
|2596822 |2510921 |0            |
+-------------------------------+
|3000143 |2409999 |0            |
+-------------------------------+
|3125674 |2409999 |0            |
................................
       the list goes on

… from which I need to build a html tree list using <ul> and <li>. Every node in this table is a child of top node with id 1000000 (which has Parent “-1”). Also, HasChildren “-1” tells that this node has children, 0 – it has not. Yes, it’s kinda weird convention, but it’s as it is. So, the output should be like this:

<ul>
  <li>2409999</li>
  <ul>
    <li>3000143</li>
    <li>3125674</li>
  </ul>
  <li>2510921</li>
  <ul>
    <li>2596822</li>
  </ul>
....
</ul>

Perhaps someone has tackled the very same problem? Any help would be appreciated. Thanks!

Answer 1

As mentioned above, it would make sense to use a nested set representation in your table. If you decide to keep the existing table structure, then the general way of doing it is to have a recursive function along the lines of:

function printBranch($parentID) {
    foreach ($children as $child) {
        if ($child is a Leaf) echo '<li>child</li>';
        elseif ($child is a Branch) printBranch($child);
    }
}

Needless to say the code above is pseudo-code, but it should demonstrate the general idea. The function executes on a single node, and if that node has children it calls itself on each of the children. That is called recursion. As a common programming convention: nodes that have children are called branches, and the ones that don’t are called leafs.