PHP / MySQL build tree menu

Question

I am trying to build an un-oredered list menu tree from my database in PHP and MySQL.

I have an array of page objects I am returning from the db. Each page object

Answer 1

I like @mario's solution, and have improved on it with the prevention of the excess

. I would just recommend doing an ORDER BY on your SQL query to get the menu in the order you want (might even recommend a weight/sequence column be added to the schema.

Data setup:

$menu = array( // Presumed to have been coming from a SQL SELECT, populated for demo.
  array('id'=>1,'title'=>'Menu 1',          'parent_id'=>null),
  array('id'=>2,'title'=>'Sub 1.1',         'parent_id'=>1),
  array('id'=>3,'title'=>'Sub 1.2',         'parent_id'=>1),
  array('id'=>4,'title'=>'Sub 1.3',         'parent_id'=>1),
  array('id'=>5,'title'=>'Menu 2',          'parent_id'=>null),
  array('id'=>6,'title'=>'Sub 2.1',         'parent_id'=>5),
  array('id'=>7,'title'=>'Sub Sub 2.1.1',   'parent_id'=>6),
  array('id'=>8,'title'=>'Sub 2.2',         'parent_id'=>5),
  array('id'=>9,'title'=>'Menu 3',          'parent_id'=>null),
);

Handling:

function has_children($rows,$id) {
  foreach ($rows as $row) {
    if ($row['parent_id'] == $id)
      return true;
  }
  return false;
}
function build_menu($rows,$parent=0)
{  
  $result = "
";
  foreach ($rows as $row)
  {
    if ($row['parent_id'] == $parent){
      $result.= "
{$row['title']}";
      if (has_children($rows,$row['id']))
        $result.= build_menu($rows,$row['id']);
      $result.= "
";
    }
  }
  $result.= "
";

  return $result;
}
echo build_menu($menu);

Output:

  
Menu 1

    
Sub 1.1
    
Sub 1.2
    
Sub 1.3
  
  
Menu 2

    
Sub 2.1

      
Sub Sub 2.1.1
    
    
Sub 2.2
  
  
Menu 3