Echo menu tree with recursive function

Question

Problem: I can\'t think of way make a recursion function to my specific situation.

Situation:

Mysql DB
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Answer 1

How about:

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            $ret .= $this->recurse($categories, $category['id'], $level+1);
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

This function requires that you first query your database for the entire list of available categories and assumes that your root categories have a value of null, but the function can be changed to accept -1 or 0 depending on how your current schema works.

$categories = { get from database into an multi-dimensional array };
$Tree = $this->recurse($categories);
echo $Tree;

You may consider doing the following to prevent any empty UL's appearing when no children exist for the parent:

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            $sub = $this->recurse($categories, $category['id'], $level+1);
            if($sub != '<ul></ul>')
                $ret .= $sub;
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

However, the best solution, would be to select your data to include a column containing how many child categories each category has.

select Category.*, (select count(distinct c1.id) from Category as c1 where c1.root = Category.id) as ChildCount from Category

In which your function would be:

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            if($category['ChildCount'] > 0)
                $ret .= $this->recurse($categories, $category['id'], $level+1);
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

Hope that helps?