function to display menu from a set level

Question

I have a function that retrieves menu data from Magento and outputs it to a javascript front-end.

  public function getMenuData()
    {
        if (!is_null($this->_menuData)) return $this->_menuData;
        $blockClassName = Mage::getConfig()->getBlockClassName('custommenu/navigation');
        $block = new $blockClassName();
        $categories = $block->getStoreCategories();
        if (is_object($categories)) $categories = $block->getStoreCategories()->getNodes();
        if (Mage::getStoreConfig('custom_menu/general/ajax_load_content')) {
            $_moblieMenuAjaxUrl = str_replace('http:', '', Mage::getUrl('custommenu/ajaxmobilemenucontent'));
            $_menuAjaxUrl = str_replace('http:', '', Mage::getUrl('custommenu/ajaxmenucontent'));
        } else {
            $_moblieMenuAjaxUrl = '';
            $_menuAjaxUrl = '';
        }
        $this->_menuData = array(
            '_block'                        => $block,
            '_categories'                   => $categories,
            '_moblieMenuAjaxUrl'            => $_moblieMenuAjaxUrl,
            '_menuAjaxUrl'                  => $_menuAjaxUrl,
            '_showHomeLink'                 => Mage::getStoreConfig('custom_menu/general/show_home_link'),
            '_popupWidth'                   => Mage::getStoreConfig('custom_menu/popup/width') + 0,
            '_popupTopOffset'               => Mage::getStoreConfig('custom_menu/popup/top_offset') + 0,
            '_popupDelayBeforeDisplaying'   => Mage::getStoreConfig('custom_menu/popup/delay_displaying') + 0,
            '_popupDelayBeforeHiding'       => Mage::getStoreConfig('custom_menu/popup/delay_hiding') + 0,
            '_rtl'                          => Mage::getStoreConfig('custom_menu/general/rtl') + 0,
            '_mobileMenuEnabled'            => Mage::getStoreConfig('custom_menu/general/mobile_menu') + 0,
            '_mobileMenuWidthInit'          => Mage::getStoreConfig('custom_menu/general/mobile_menu_width_init') + 0,
        );
        return $this->_menuData;
    }

I've been trying to find a way to modify it so that I can alter the depth of the menu being initially displayed.

I've tried changing the $categories variable over to a call to

Mage::getModel('catalog/category')->getCollection()->addAttributeToSelect('*')->addAttributeToFilter('level', array('eq'=>3))->addAttributeToFilter('parent_id',array('eq' => $parent_cat_id))->load();

to try and force it to show categories at level 3 whose parent is set by the category ID, but for the life of me I just cant crack this at the moment.

Answer 1

To get all children for a given category $parent_cat_id, use this code:

// load parent if you only have the ID:
$parent = Mage::getModel('catalog/category')->load($parent_cat_id);
// get array of child categories (not a collection!)
$categories = $parent->getChildrenCategories()

All children of a category with level 2 are level 3, so no additional filtering of the level is necessary.

Answer 2

In the end it was simpler to create a new menu using existing Magento calls, rather than reverse engineering the existing, however a few bits of code from fscmengler did help in creating this!

I'll try and remove the markdown code to display the structure I came up with in the end as it works quite well!