Magento - get categories and subcategories in a collection - magento

Question

I have the following category structure in my magento store
- root
- category 0 (ID 26)
- category 1 (main)
- category A (sub)
- category V (sub)
- category 2 (main)
- category G (sub)
- category J (sub)
- category E (sub)
- category 3 (main)
- category L (sub)
and so on...
On a page i want to be able to output the following:
1. get each (main) category and its name and url
2. get the first (sub) category in (main) and its icon (custom attribute)
So it would output this for each:
<img src="main-cat-first-sub-icon">
main-cat-name
Giving something like:
<category 1 link><category A icon img></link>
<category 1 link><category 1 name>
<category 2 link><category G icon img>
<category 2 link><category 2 link>
<category 3 link><category L icon img>
<category 3 link><category 3 link>
What is the best way of doing so? So far I have:
<?php
$_id = 26 // category 0
$_main_categories = Mage::getModel('catalog/category')
->getCollection()
->addFieldToFilter('parent_id', array('eq'=>$_id))
->addAttributeToFilter('is_active', 1)
->addAttributeToSelect(array('id','name','url'))
foreach($_main_categories as $_main_cat)
{
// load full main category
$_category = Mage::getModel('catalog/category')->load($_main_cat->getId());
// get sub category's children
$_main_cat_subs = $_category->getChildrenCategories();
// loop through sub catagories, get icon in first and break
foreach($_main_cat_subs as $_sub_cat)
{
// load full sub category
$_sub = Mage::getModel('catalog/category')->load($_sub_cat->getId());
$i++;
$_icon = $_sub_cat->getIcon();
}
if( $i >= 1 ){
break; // as i only want the first one
}
}
// output
?>
<a href="<?php echo $_main_cat->getUrl() ?>">
<img src="<?php echo $_icon ?>">
</a>
<a href="<?php echo $_main_cat->getUrl() ?>">
<?php echo $_main_cat->getName() ?>
</a>
<?php
}
?>
This works but seems very bad practice to load the full category models in a foreach loop twice and when the site grows could take a long time.
What is the best way of doing the above performance wise?

Answer 1

What you could optimize is this:
$_category = Mage::getModel('catalog/category')->load($_main_cat->getId());
Here you are loading the category (again) from the database. Though you already loaded a collection, you should put all the categories you need in that collection with the right attributes.
Then instead of the code above, use this handful collection function to get the category entity:
$_category = $_main_categories->getItemById($_main_cat->getId());
//...
$_sub = $_main_categories->getItemById($_sub_cat->getId());
You should see a clear improvement in the performance, especially if you have a lot of categories.