How to conditionally redirect to the post from a taxonomy page?

Question

I would like to redirect to a post if the taxonomy term it belongs to has only one post assigned to it and so far I have this:

$term_id = get_queried_object()->term_id;
$taxonomy_name = 'product_range';
$term_children = get_term_children( $term_id, $taxonomy_name );

foreach ( $term_children as $child ) {
  $term = get_term_by( 'id', $child, $taxonomy_name );
    if($term->count <= 1 ) {
      echo '<a href="'. get_term_link($child, $taxonomy_name) .'" class="thumb" title="'.$term->name.'">'.$term->name.'</a>';
    }
}

This links through to the archive page but I want it to redirect the user to the relevant post, I am not sure what I need to do to change the permalink to go to the single post page.

Answer 1

I think you can simply use WP_Term's $count property which should hold the number of posts attached to this current term.
Then, if only one post is attached to this term, query this post object and do your stuff with it...

$term = get_queried_object();

if ( $term->count === 1 ) {
    $args = array(
        'tax_query' => array(
            array(
                'taxonomy'         => 'product_range',
                'field'            => 'term_id',
                'terms'            => array( $term->term_id ),
                'include_children' => false,
            ),
        )
    );

    $query = new WP_Query( $args );
    $posts = $query->posts;
    $post  = $posts[0];

    /**
     * IMPORTANT FOR SEO...
     * Temporary redirection until your category is populated - Use 301 instead of 302 to redirect permanently...
     */
    if ( wp_redirect( get_permalink( $post->ID ), 302 ) ) {
        exit;
    }
}

Answer 2

@ClemC I managed to figure this out by adding a WP_Query to query the posts and check the count, here is my code:

    $term_id = get_queried_object()->term_id;
        $taxonomy_name = 'product_range';
        $custom_terms = get_term_children( $term_id, $taxonomy_name );
            echo '<div class="row row__condensed">';
            foreach($custom_terms as $custom_term) {
                $term = get_term_by( 'id', $custom_term, $taxonomy_name );
                wp_reset_query();
                $args = array(
                    'post_type' => 'product',
                    'posts_per_page' => 1,
                    'tax_query' => array(
                        array(
                            'taxonomy' => 'product_range',
                            'field' => 'slug',
                            'terms' => $term->slug,
                        ),
                    ),
                 );

                $loop = new WP_Query($args);

                if($loop->have_posts()) {

                    while($loop->have_posts()) : $loop->the_post();
                        // If only one post exists link to product
                        if($term->count === 1 ) {
                            echo '<div class="col-xs-12 col-md-4">';
                                echo '<div class="grid__item">';
                                    echo '<a href="'.get_permalink().'">';                                                       
                                    echo '</a>';
                                    echo '<h3><a href="' . get_permalink() . '">'.$term->name .'</a></h3>';
                                    echo '<p>'.wp_trim_words($term->description, 23, '...').'</p>';
                                echo '</div>';
                            echo '</div>';
                        }
                        //else link to the listing page
                        else {
                            echo '<div class="col-xs-12 col-md-4">';
                                echo '<div class="grid__item">';
                                    echo '<a href="' . get_term_link( $custom_term, $taxonomy_name ) . '">';                                    
                                    echo '</a>';
                                    echo '<h3><a href="' . get_term_link( $custom_term, $taxonomy_name ) . '">'.$term->name .'</a></h3>';
                                echo '<p>'.wp_trim_words($term->description, 23, '...').'</p>';
                                echo '</div>';
                            echo '</div>';
                        }
                    endwhile;
                }
            else {
        echo "no posts found.";
            } //endforeach
        echo '</div>';