Creating a PHP/MySQL Tree

class TreeViewBuilder
  /**
   * build the current node
   * @param NodeDao
   * @param Node
   * @return string  html string
   */
  public method buildNode (NodeDao $O_dao, Node $O_node)
  {
     $S_html = '';
    /** [... here the code to build current cliquable node ($S_html), using info returned by Node object accessors...] */

    //are there children?
    $A_nodeList = $o_dao->getChildren($O_node);

    foreach ($A_nodeList as $O_childNode){
      $S_html .= $this->buildNode($O_dao, $O_childNode);// this the recursive call to the same build method foreach child found
    }

      return $S_html;
  }
}

class NodeDao
{
  /**
   * find a Node in DB
   * @param Node
   * @return Node
   */
  public function find(Node $O_node)
  {
    if(!$O_node->getId()) {
      throw new Exception ('Node object should have an Id');
    }

    $S_sql = 'select ..... where node = \'' . mysql_real_escape_string($O_node->getId()) . '\'';
    $recordset = mysql_query($S_sql);
    if($A_row = mysql_fetch_assoc($R_recordset))
    {
      $O_nodeFind = clone $O_node;

      $O_nodeFind->setName($A_row['nodename']);
      $O_nodeFind->setLink($A_row['nodelink']);
      //etc.

      return $O_nodeFind;
    }
    else {
      throw new Exception ('Node "' .$node->getId(). '" not Find');
    }

    return $nodeFind;
  }

  /**
   * Find the children of a given node
   * @param Node
   * @return Node
   */
  public function getChildren(Node $O_parent)
  {
    if(!$O_parent->getId()) {
      throw new Exception ('Parent Node object should have an Id');
    }

    $A_found = array();



    $S_sql = 'select ..... where prevnode = \'' . mysql_real_escape_string($O_parent->getId()) . '\'';
    $R_recordset = mysql_query($S_sql);

    while($A_row = mysql_fetch_assoc($R_recordset))
    {
      $O_nodeFind = clone $node;
      $O_nodeFind->setId($A_row['node']);
      $O_nodeFind->setName($A_row['nodename']);
      $O_nodeFind->setLink($A_row['nodelink']);
      //etc.
      $A_found[$O_nodeFind->getId()] = $O_nodeFind;
    }

    return $A_found;
  }

  //etc. use Node accessor for whrite methods like create (for insertion), delete, update

class Node
{
  protected $_S_id://node ID
  protected $_S_name;
  protected $_S_prev;
  //etc.

  /**
   * allows to get node Id
   * @return string
   */
  public function getId()
  {
    return $this->_S_id;
  }

  /**
   * allows to set node Id
   * @param string
   */
  public function setId($S_id)
  {
    $this->_S_id = (string) $S_id;
  }

  //etc.
}