custom url for navigation menu

[amstatonline]

I am trying to create a module so that you can define a custom url for the navigation menu. I am trying to link to a non CMS page created by another extension. I was able to create the custom attribute for the category and it shows in admin but when I try to extend "Mage_Catalog_Model_Category" to overwrite the "getUrl" function, I am not able to access my new custom attribute. See below for code. I just want to use the "custom_category_url" if there is a value otherwise fallback to the parent getUrl function, but currently $this->getData('custom_category_url') is always returning NULL. I assume I need to do something so that the attribute is available at this point but I am not sure how. Full code is available at https://github.com/americanstationery/AmstatCustomUrl.

<?php
class Amstat_CustomUrl_Model_Category extends Mage_Catalog_Model_Category
{
    /**
     * Get category url
     *
     * @return string
     */
    public function getUrl()
    {
        $categoryRedirectUrl = $this->getData('custom_category_url');
 
        if(strlen($categoryRedirectUrl) > 0 && $categoryRedirectUrl != '0'){
            return $categoryRedirectUrl;
        }

        return parent::getUrl();
    }
}

[Tom Robertshaw]

I haven't tried the code but it could be because the attribute is marked to be "used_in_product_listing" => "true" and so isn't added to the flat table. If the category is being loaded from the flat category table without this setting then it wouldn't be available.