PHP sitemap using a tree data structure

I was once asked to create a sitemap given a specific table structure.

This was the structure(the table):

The resulting sitemap as I understood it was supposed to look something like this:

The parenthesis after the titles actually hold the value of the id of the node so they weren't in the original design but whatever.

So I implemented this in PHP using a tree data structure where each node held 3 pieces of information:

id - the current node's id as read from the database

parent_id - the current node's parent id as read from the database

title - the title

A real-world implementation would also have to include a link and print out elements but this is good enough for educational purposes.

Each node also holds an array of subnodes.

This is the database information read to create the tree:

CREATE TABLE IF NOT EXISTS `sitepages` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`id_parent` int(11) unsigned NOT NULL,
`title` varchar(100) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

INSERT INTO `sitepages` (`id`, `id_parent`, `title`) VALUES
(1, 0, 'Home'),
(2, 1, 'Page 1'),
(3, 0, 'Page 2'),
(4, 1, 'Page 3'),
(5, 3, 'Page 4'),
(6, 1, 'Page 5'),
(7, 4, 'Page 6'),
(8, 7, 'Page 7'),
(9, 5, 'Page 8');

I used to php classes to represent the tree. One to represent a node of the tree and one for the tree itself:

This is for the node:

//a node of a tree that is not binary, each nodes has multiple subnodes 
class Node 
{  
public $id;  
public $id_parent;  
public $childnodes;  
public $title;    

public function __construct($id,$id_parent,$title)  
{   
//in the test script I use mysql_fetch_object which populates the members and then //calls the constuctor with all    
//parameters as null   
//the following checks are here to make sure no members are accidentally overriden
      
if(!isset($this--->id))
  $this->id = $id;

 if(!isset($this->id_parent))  
  $this->id_parent = $id_parent;

 if(!isset($this->title))  
  $this->title = $title;

 if(!isset($this->childnodes))  
  $this->childnodes = array();
}

//check if this node has subnodes or not
public function hasChildren()
{
 if($this->childnodes === null)
  return false;

 if(!isset($this->childnodes))  
  return false;

 if(count($this->childnodes) == 0)
  return false;

 return true;
}
}

This is the tree:

require("node.class.php");  
class Tree 
{  

private $root;   

//construct a tree with only one root node  public function __construct()  
{   
$this->root = new Node(0,0);
}

//recursively traverse the tree looking for the appropiate parent id
//the node to be inserted($node) must have a parent id equal to one of the ids in the nodes of the tree
//if such an id is found in a node the node is included as a subnode of that node
private function addNodeRecursive(&$nextnode,$node)
{
 if($nextnode == null)
  return false;
 
 if($nextnode->id == $node->id_parent)
 {
  array_push($nextnode->childnodes,$node);
  return true;
 }
 else
 {
  if($nextnode->hasChildren())
  {
   foreach ($nextnode->childnodes as $childnode)
   {
    $this->addNodeRecursive($childnode,$node);
   }
   return false;
  }
  else
   return false;
 }
}

//add a node to the tree
//check if it is a valid node start at the root and recursively traverse the tree looking for the appropiate parent id
public function addNode($node)
{
 if(!($node instanceof Node))
  return;

 $nextnode = $this->root;

 $this->addNodeRecursive($nextnode,$node);
}

//print the tree in sitemap style
public function printSiteMap()
{
 foreach($this->root->childnodes as $childnode)
 {
  $this->printTree($childnode,0);
 }
}

//print the tree recursively
//first print the current node's value and then print the cycle through it's subnodes
public function printTree(&$nextnode,$level)
{
 $this->printNodeAccordingToLevel($nextnode,$level);

 if($nextnode->hasChildren())
 {
  foreach($nextnode->childnodes as $childnode)
  {
   $this->printTree($childnode,$level+1);
  }
 }
}

//add the appropiate number of   before each node value so as to obtain a nicely formatted sitemap
//each node value is indented with respect to the node's level
private function printNodeAccordingToLevel($node,$level)
{
 for($i=0;$i<$level;$i++)    echo " ";    echo $node->title."(".$node->id.")";
 
 echo "
";
}

}

And this is a test just to make sure everything works:

require("tree.class.php");  
$tree = new Tree();  
if(!($conn = mysql_connect("localhost","root",""))) 
{  
echo "Could not connect";  
exit; 
}  
if(!mysql_selectdb("sitemap")) 
{  
echo "No such database";  
exit; 
}  
if($result = mysql_query("SELECT id,id_parent,title FROM sitepages")) 
{  
while ($page = mysql_fetch_object($result,'Node'))   
$tree->addNode($page);
}

$tree->printSiteMap();