Algorithm to Save Items with Parent-Child Relationship to Database

Question

I need help designing the logic of an app that I am working on. The application should enable users to create mindmaps and save them to a mysql database for later editing. Each mindmap is made up of inter-related nodes, meaning a node should have a parent node and the id of the mindmap to which it belongs. I am stuck here. How can I save the nodes to the database and be able to query and rebuild the mindmap tree from the query results.

Root
   Child1
   Child2
      GrandChild1
    GreatGrandChild1
    GreatGrandChild1
   Child3
      GrandChild2

I need an algorithm, that can save the nodes and also be able to figure out the relationships/order of items similar to the Tree that I have given. This is very much like how menus are saved and retrieved in Wordpress but I can't find the right logic to do this. I know there are really great people here. Please help.

Answer 1

I finally found a solution. Here's my full code.

require_once('config.php');//db conn
$connect = mysql_connect(DB_HOST, DB_USER, DB_PASS);
mysql_select_db(DB_NAME);
$nav_query = MYSQL_QUERY("SELECT * FROM `nodes` ORDER BY `id`");
$tree = "";                         // Clear the directory tree
$depth = 1;                         // Child level depth.
$top_level_on = 1;               // What top-level category are we on?
$exclude = ARRAY();               // Define the exclusion array
ARRAY_PUSH($exclude, 0);     // Put a starting value in it

WHILE ( $nav_row = MYSQL_FETCH_ARRAY($nav_query) )
{
     $goOn = 1;               // Resets variable to allow us to continue building out the tree.
     FOR($x = 0; $x < COUNT($exclude); $x++ )          // Check to see if the new item has been used
     {
          IF ( $exclude[$x] == $nav_row['id'] )
          {
               $goOn = 0;
               BREAK;                    // Stop looking b/c we already found that it's in the exclusion list and we can't continue to process this node
          }
     }
     IF ( $goOn == 1 )
     {
          $tree .= $nav_row['name'] . "<br>";                    // Process the main tree node
          ARRAY_PUSH($exclude, $nav_row['id']);          // Add to the exclusion list
          IF ( $nav_row['id'] < 6 )
          { $top_level_on = $nav_row['id']; }

          $tree .= build_child($nav_row['id']);          // Start the recursive function of building the child tree
     }
}

FUNCTION build_child($oldID)               // Recursive function to get all of the children...unlimited depth
{
    $tempTree='<ul>';
     GLOBAL $exclude, $depth;               // Refer to the global array defined at the top of this script
     $child_query = MYSQL_QUERY("SELECT * FROM `nodes` WHERE parent_id=" . $oldID);
     WHILE ( $child = MYSQL_FETCH_ARRAY($child_query) )
     {
          IF ( $child['id'] != $child['parent_id'] )
          {
               FOR ( $c=0;$c<$depth;$c++ )               // Indent over so that there is distinction between levels
               { $tempTree .= "&nbsp;"; }
               $tempTree .= "<li>" . $child['name'] . "</li>";
               $depth++;          // Incriment depth b/c we're building this child's child tree  (complicated yet???)
               $tempTree .= build_child($child['id']);          // Add to the temporary local tree
               $depth--;          // Decrement depth b/c we're done building the child's child tree.
               ARRAY_PUSH($exclude, $child['id']);               // Add the item to the exclusion list
          }
     }

     RETURN $tempTree.'</ul>';          // Return the entire child tree
}

ECHO $tree;

?>

This is based on the piece of code found here http://psoug.org/snippet/PHP-Recursive-function-to-generate-a-parentchild-tree_338.html I hope this helps someone as well