[technobard]

I have written a solution based on my earlier outline. As Scott pointed out, there are other ways of doing this. This is a single parent model. It can be extended to include multiple parents with some (what I believe to be) minor modifications.

I learned a few things about references (not quite pointers) in PHP along the way. I may write this up as a NUM.

If anyone has any questions in the meantime, let me know.

**** sample main loop for building and printing a tree structure
**** include file to follow for Hierarchy class

<?
include "hierarchy.inc";
$username = "user";
$password = "pass";
$databasename = "test";

$link = mysql_connect($hostname, $username, $password);
mysql_select_db($databasename, $link);

$stmt = "select id, parent_id, description from hierarchy";
$result = mysql_db_query($databasename, $stmt);

$object = array();  /* lookup table of references to objects */

//$object["0"] = new Hierarchy(0);   -- will be added automatically
//$object["0"]->setDesc("root");

while ($row = mysql_fetch_object($result)) {
   if (is_null($object["$row->id"])) {   /* if object doesn't already exist  */
      $tmp_obj = &new Hierarchy($row->id);
   } else {
       $tmp_obj = &$object["$row->id"];     /* lookup existing object */
   }
      $tmp_obj->setParent_id($row->parent_id);
      $tmp_obj->setDesc($row->description);

      $object["$row->id"] = &$tmp_obj;    /* add object reference to lookup
table  */

   if (is_null($object["$row->parent_id"])) {   /* if parent doesn't already exist,
create it */
      $tmp_obj2 = &new Hierarchy($row->parent_id);
      $object["$row->parent_id"] = &$tmp_obj2;
   } else {
      $tmp_obj2 = &$object["$row->parent_id"];
   }

   $tmp_obj2->addChild($row->id);

}  /* end of while loop to load data */

mysql_free_result($result);   /* free resultset */

/* print entire tree starting at root node - 0 */

$object[0]->printChildren(0, $object);


?>

*** include file "hierarchy.inc" ***
The Hierarchy Class (each node with a list of it's children)

<?

class Hierarchy {
   var $id;
   var $parent_id;
   var $description;
   var $children;
   var $level;

   function Hierarchy($new_id) {
      $this->setId($new_id);
      $this->children = array();
   }


   function setId($new_id) {
      $this->id = $new_id;
   }

   function setParent_id($newParent_id) {
      $this->parent_id = $newParent_id;
   }

   function setDesc($desc) {
      $this->description = $desc;
   }

   function addChild($child_id) {
      $this->children[] = $child_id;
   }

   function printDesc($num_tabs) {
      $tab = "&amp;nbsp; &amp;nbsp; &amp;nbsp;";
      
      for ($i=1; $i<=$num_tabs; $i++ ) {
         $tabs = $tabs.$tab;
      }
      print $tabs.$this->description;
      print "<BR>";
   }

   function printChildren($tree_lvl, &$hashtab) {
      /* loop through array of $children, print $description, */
      /* call printChildren(); stop when all children are processed */
      
     $this->level = $tree_lvl;

     foreach ($this->children as $child) {
         $hashtab["$child"]->printDesc($this->level + 1);
         $hashtab["$child"]->printChildren($this->level + 1,$hashtab);
     }
   }

}

?>