How to get root category

[bi0xid]

I have looking for some function that allow me to know whick is the root category of one given category when we have a category tree.

I found only how to get the parent category, but not the root, so I made this function for one of my projects:

function get_category_root($category_id){
	$category = $category_id->cat_ID;
    global $wpdb;
    	$parent = $wpdb->get_var( "SELECT parent FROM $wpdb->term_taxonomy WHERE term_id = '$category'");
		if ($parent == 0) {
			return $category;
		}
		while ($parent != 0){
			$category = $parent;
			$parent = $wpdb->get_var( "SELECT parent FROM $wpdb->term_taxonomy WHERE term_id = '$category'");
			if ($parent == 0) {
				return $category;
			}else{
				$category = $parent;
			}
		}
}

Maybe it's useful.

[filosofo]

I think the function as above will give you some problems. First, there could be more than one entry for a term_id in term_taxonomy. You really need to specify the taxonomy or (better yet) just let the WordPress API handle it for you. Also, if something is a category ID (an integer), then it won't have an object property of "cat_ID", so $category_id->cat_ID will probably produce a PHP notice, at least.

I think this should do the same thing:

function get_category_root($cat_id = 0) {
        $category_parent = get_category($cat_id);
        while( ! empty( $category_parent->category_parent ) ) { 
                $category_parent = get_category($category_parent->category_parent);
        }   
        return ! empty( $category_parent->term_id ) ? $category_parent->term_id : $cat_id;
}

What would be more useful in my opinion would be a function that, given a term ID and a particular taxonomy, returns an array of IDs of that term's ancestors, in order. That way you could easily get the root ancestor, but you could also easily check for the presence of any term ancestor.

[bi0xid]

It's working in my very concrete installation with its special features. But, of course, it had a lot of fails.

Thanks a lot! I'm testing it.

And agree with the root ancestor function.

[bi0xid]

Category with get_root_category

[bi0xid]

Trying to get this solved.

[hakre]

I like the Idea to have such a function but as said, this needs to be implemented properly. At least endless recursion must be successfully prevented. Database should be taken into considerations to not make such a function more expensive than it must be.

[bi0xid]

Replying to hakre:

I like the Idea to have such a function but as said, this needs to be implemented properly. At least endless recursion must be successfully prevented. Database should be taken into considerations to not make such a function more expensive than it must be.

I have used filosofo's implementation in .diff. I think it prevents endless recursion and database problems. What do you think?

[hakre]

Replying to bi0xid:

I have used filosofo's implementation in .diff. I think it prevents endless recursion and database problems. What do you think?

It will create and endless loop given the following data:

Cat1->parent = Cat2
Cat2->parent = Cat3
Cat3->parent = Cat1

calling get_category_root($cat_id = id of Cat1) will create an endless loop.

Maybe that gives you an idea. What I like is that it resolves linear so far.

[hakre]

Related: #8384

[scribu]

See #12908