How can I get parent term from a child term

Question

I have a custom post type and a taxonomy, when adding a post if I select a child term and not the parent term then I cannot use get terms as the parent term wont be in the array as it wasn't selected so I was wondering if it possible to get the parent term/id using a child term?

As I was to do an if statement so that if a single post parent term is (id 4) then display something.

So I need to get terms (all of which will be a child term and using the child term get the parent term for that term)

Answer 1

Inside the loop you can make use of wp_get_post_terms() to return all the terms associated with the specific post. This object returned holds all the terms with all the properties of the specified terms

With that in mind, you can use a foreach loop to get each term, and then check each term's parent. For grandchild terms you will need to do some extra checking here to determine the parent or top most level term parent

You can do something like this

$terms = wp_get_post_terms( $post->ID, 'category' );
if ( !empty( $terms ) && !is_wp_error( $terms ) ){
    foreach ( $terms as $term ) {
        if ( $term->parent == 4 ) {
            //Do something if parent is 4
        }
    }
}

EDIT

To make this work with deeper level categories, you can use get_ancestors() to get all levels and use in_array() to test for the specific category ID

You can extend the function as follow:

$terms = wp_get_post_terms( $post->ID, 'category' );
if ( !empty( $terms ) && !is_wp_error( $terms ) ){
    foreach ( $terms as $term ) {
        if( $term->parent != 4 && $term->parent == 0 )
            continue;

        if ( $term->parent == 4 || in_array( 4, get_ancestors( $term->term_id, 'category' ) )) {
            //Do something if parent ID is 4
        } else {
            //Do nothing
        }
    }
}