PHP Category Reverse Traversal Algorithm

Question

I'm trying to optimize an e-commerce category system with unlimited category depth (barring system memory limitations). I retrieve all the categories at once and order them as a multi-dimensional array that roughly looks like:

[array] (
  [0] (
    'CategoryId' => 1,
    'ParentCategoryId' => 0,
    'Title' => 'Category A',
    'SubCategories' => [array] (
      [0] (
        'CategoryId' => 2,
        'ParentCategoryId' => 1,
        'Title' => 'Category B',
        'SubCategories' => [array] (
          [0] (
            'CategoryId' => 3,
            'ParentCategoryId' => 2,
            'Title' => 'Category C'
          )
        )
      )
    )
  )
)

Each item in the array is actually an object, but for simplicity I wrote it out kind of like an array format.

I'm able to traverse my tree downwards using this function:

/**
* Find Branch using Recursive search by Object Key
* @param String     Needle
* @param Array      Haystack
* @return Array
*/
public static function findBranchByKey($key, $needle, $haystack)
{
    foreach ($haystack as $item) 
    {
        if ( $item->$key == $needle || ( is_object($item) && $item = self::findBranchByKey($key, $needle, $item->SubCategories)) ) 
        {
            return $item;
        }
    }
    return false;
}

This finds the object with a matching key and returns it (which may contain more subcategories).

My issue is figuring out how to traverse the other direction. For example, using the data above, let's say I am displaying "Category C" and want to create bread crumbs of it's parents. I can't think of a good way to take my tree array, jump to a specific subcategory, then iterate upwards to get each parent. A resulting array from something like this could be like this so it's easy to spit them out as bread crumbs:

 array( 'Category A', 'Category B', 'Category C' )

I could probably do this using SQL in my database but I'd like to retrieve the tree once, cache it, and perform traversal on that object whenever I need to rather than making tons of queries.

TL;DR; How can I traverse upwards in a multidimensional array of categories?

Answer 1

It can be done by recursion.

Let's say, this function should work:

function getPath($id, $tree, &$path = array()) {
    foreach ($tree as $item) {
        if ($item['CategoryId'] == $id) {           
            array_push($path, $item['CategoryId']);
            return $path;
        }
        if (!empty($item['SubCategories'])) {
            array_push($path, $item['CategoryId']);
            if (getPath($id, $item['SubCategories'], $path) === false) {
                array_pop($path);
            } else {
                return $path;
            }

        }
    }
    return false;
}

This:

$data = array(
    array(
        'CategoryId' => 10,
        'ParentCategoryId' => 0,
        'SubCategories' => array(
            array(
                'CategoryId' => 12,
                'ParentCategoryId' => 1,
                'SubCategories' => array()
            ),
        )
    ),
    array(
        'CategoryId' => 1,
        'ParentCategoryId' => 0,
        'SubCategories' => array(
            array(
                'CategoryId' => 2,
                'ParentCategoryId' => 1,
                'SubCategories' => array()
            ),
            array(
                'CategoryId' => 3,
                'ParentCategoryId' => 1,
                'SubCategories' => array()
            ),
                        array(
                'CategoryId' => 4,
                'ParentCategoryId' => 1,
                'SubCategories' => array(
                    array(
                        'CategoryId' => 5,
                        'ParentCategoryId' => 4,
                        'SubCategories' => array()
                    ),
                )
            )
        )
    )
);

$result = getPath(5, $data);
print_r($result);

will result in:

Array ( [0] => 1 [1] => 4 [2] => 5 )