has_category() for parent category

Question

Is there a way to make a condition for posts belonging to any sub-categories of a given parent category? Here is an example, assuming the following category structure:

• News
• FAQ
  • 1) Installing
  • 2) Using, etc.
• Other

if ( has_category( 'FAQ' ) ) { 
    echo "This page has been updated for Quick Access Popup v10.";
}
else {
    echo "This page has NOT been updated for Quick Access Popup v10 yet.";
}

The has_category() condition includes only posts that are in the category 'FAQ' itself, but not those in its subcategories. I know I could use an array and list every categories but this is not convenient and need to be maintained when subcategories are added, removed, etc.

The has_category() doc says nothing about parent categories (https://developer.wordpress.org/reference/functions/has_category/)

Thanks.

Answer 1

To do what you want, you'll need to get a list of all the child categories of the category you want, and then check those. But you don't need to write that list manually. You can use get_term_children() to get the IDs of the child and grandchild categories:

$cat_id   = get_cat_ID( 'FAQ' );
$children = get_term_children( $cat_id, 'category' );

if ( has_category( $cat_id ) || has_category( $children ) ) {

}