CakePHP: formatResults() and combine() - cakephp

Question

Suppose I have this find():
$categories = $this->Pages->Categories->find('active')
->select(['title', 'slug', 'page_count'])
->order(['title' => 'ASC'])
->cache('widget_categories')
->toArray();
Now, I want the slug field will be the array key.
For now I use a (horrible) loop:
foreach ($categories as $k => $category) {
$categories[$category->slug] = $category;
unset($categories[$k]);
}
Example of debug for $categories:
########## DEBUG ##########
[
'first-page-category' => object(MeCms\Model\Entity\PagesCategory) {
'title' => 'First page category',
'slug' => 'first-page-category',
'page_count' => (int) 1,
'[new]' => false,
'[accessible]' => [
'*' => true
],
'[dirty]' => [],
'[original]' => [],
'[virtual]' => [],
'[errors]' => [],
'[invalid]' => [],
'[repository]' => 'MeCms.Categories'
},
'sub-sub-page-category' => object(MeCms\Model\Entity\PagesCategory) {
'title' => 'Sub sub page category',
'slug' => 'sub-sub-page-category',
'page_count' => (int) 2,
'[new]' => false,
'[accessible]' => [
'*' => true
],
'[dirty]' => [],
'[original]' => [],
'[virtual]' => [],
'[errors]' => [],
'[invalid]' => [],
'[repository]' => 'MeCms.Categories'
}
]
###########################
This creates two problems:
it's a horrible method;
the data is cached before changing the array keys, then the same cycle must be performed each time.
One possible solution is to use Cache::read() and Cache::write(). Example:
$categories = Cache::read('widget_categories');
if (empty($categories)) {
//Find...
//Loop for changing keys...
Cache::write('widget_categories', $categories);
}
What seems to me the best solution, however, it is to use formatResults() with combine() methods. Example:
$categories = $this->Pages->Categories->find('active')
->select(['title', 'slug', 'page_count'])
->order(['title' => 'ASC'])
->formatResults(function ($results) {
return $results->combine('slug', function ($row) {
return $row;
});
})
->cache('widget_categories')
->toArray();
It's correct? Is there a simpler method and/or makes the code more readable?
Thanks.