Related Posts: Notice: Undefined offset: 0

Question

I get an undefined Offset message with this Query. Can anyone Help?

$terms = get_the_terms( $post->ID , 'filters', 'string');
        $term_ids = wp_list_pluck($terms,'term_id');
        $second_query = new WP_Query( array(
              'post_type' => 'portfolio',
              'tax_query' => array(
                            array(
                                'taxonomy' => 'filters',
                                'field' => 'id',
                                'terms' => $term_ids,
                                'operator'=> 'IN' //Or 'AND' or 'NOT IN'
                             )),
              'posts_per_page' => 4,
              'ignore_sticky_posts' => 1,
              'orderby' => 'date',  // 'rand' for random order
              'post__not_in'=>array($post->ID)
           ) );

Answer 1

When you use wp_list_pluck on $terms what you get is an array where the key is the same as the value. If you dump the contents of $term_ids you'll see something like:

array(
    [42] => 42,
    [56] => 56
}

The code in query.php tries to reference the zero index of the term_ids array, but there is no index 0, hence the warning.

Answer 2

As Milo pointed out your array is broken (the error told you that already). To get an array WP can work with use array_values():

$term_ids = array_values( wp_list_pluck( $terms,'term_id' ) );