Finding a Category Ancestor / Descendant for WP Templates

Adrian Mummey — Wed, 11 Mar 2009 06:01:02 +0000

Recently I had a problem where I needed to find out if a specific category was a descendant of another category, or if one category was a ancestor of another. The latest website I am working on has a top level category called “Trips we do” and below that are many sub-categories and sub-sub categories etc. I wanted to use the same template on all of the categories that were descended from the “Trips we do”.
Wordpress already has a function that returns the parent categories get_category_parents but this returns a string more suited for breadcrumbs. I needed a yes or no answer that my category in question was in fact descended from some other arbitrary category. Here is the function I produced:

function is_ancestor_cat($ancestor, $descendant){
  $ancestor = (string) $ancestor;
  $desc_id = (string) $descendant;
  $child_cats = get_term_children( (string) $ancestor, 'category');
  if($ancestor == $descendant){
    return true;
  }
  else if(!count($child_cats)){
    return false;
  }
  else{
    $is_child = false;
    foreach($child_cats as $cat_id){
      if($cat_id == $desc_id){
        $is_child = true;
        break;
      }
      else{
        $is_child = $is_child || is_ancestor_cat($cat_id, $descendant);
      }
    }
    return $is_child;
  }
}

What this code does is that is grabs all the children for the ancestor category then checks them against the descendant category, it will keep recursing until it hits the leaf nodes and returns a boolean value.
Here it is in action in my template file category.php:

//Check if we are in a category
if(is_category()){
  $ancestor_cat_id = 43;
  //Lets get the current category we are in
  $cur_cat_id = get_cat_id( single_cat_title("",false) );
  $is_ancestor = false;
  //Check if we are in the ancestor category
  $is_ancestor = is_ancestor_cat($ancestor_cat_id, $cur_cat_id);

  //If it is an ancestor, use a specific template
  if($is_ancestor){
   include(TEMPLATEPATH.'/category-43.php');
  }
  //Use the default template
  else{
   include(TEMPLATEPATH.'/category-default.php');
  }

}

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Finding a Category Ancestor / Descendant for WP Templates