Related posts with WP_Query

Question

I'm stuck with the related posts querying. I need the related posts to be displayed with any depth from the main parent. I have the following structure categories on my website:

- Category level 1
-- Category level 2
--- Category level 3
*---- Post in level 3*
--- Category level 3
*--- Post in level 3*
-- Category level 2
-- Category level 2

When we looking at the *---- Post in level 3* we must see any post from the *-- Category level 2* ie all the posts that contain this level including child.

Here is my code:

<div class="related_goods">
<span>Related posts:</span>
    <?php
    $categories = get_the_category($post->ID);
    if ($categories) {
    $category_ids = array();
    foreach($categories as $individual_category) $category_ids[] = $individual_category->term_id;
    $args=array(
    'category__in' => $category_ids,
    'post__not_in' => array($post->ID),
    'showposts'=>3,
    'orderby'=>title,
    'post_parent'=> array(),
    'caller_get_posts'=>1);
    $my_query = new wp_query($args);
    if( $my_query->have_posts() ) {

    while ($my_query->have_posts()) {
    $my_query->the_post();
    ?>
    <div class="block-related-item">
        <div class="preview-wrap">
            <div class="preview">
                <? $thumb_url = wp_get_attachment_url(get_post_thumbnail_id($post->ID)); ?>
                <a href="<?php the_permalink() ?>"><? the_post_thumbnail('category_thumbs'); ?>
                </a>
            </div>
            <a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a>
        </div>          
    </div>
    <?php
    }
    }
    wp_reset_query();
    }
    ?>
</div>

How can I modify it to obtain the above effect? Thanks a lot in advance!

Answer 1

parent is your answer here. Every term have a parent value set in its parent property. This value is an integer value, and represent the term id of its parent term. All top level terms have a value of 0 which just simply means it is a top level term

First we need to build an array with parent terms and the specific terms from get_the_category. We will skip 0 values. Once we have our array of ids, we will get all unique values and pass the array of ids to a tax_query in order to save on multiple queries

(The following code is untested and require PHP 5.4+)

function get_related_category_posts()
{
    // Check if we are on a single page, if not, return false
    if ( !is_single() )
        return false;

    // Get the current post id
    $post_id = get_queried_object_id();

    // Get the post categories
    $categories = get_the_category( $post_id );

    // Lets build our array
    // If we don't have categories, bail
    if ( !$categories )
        return false;

    foreach ( $categories as $category ) {
        if ( $category->parent == 0 ) {
            $term_ids[] = $category->term_id;
        } else {
            $term_ids[] = $category->parent;
            $term_ids[] = $category->term_id;
        }
    }

    // Remove duplicate values from the array
    $unique_array = array_unique( $term_ids );

    // Lets build our query
    $args = [
        'post__not_in' => [$post_id],
        'posts_per_page' => 3, // Note: showposts is depreciated in favor of posts_per_page
        'ignore_sticky_posts' => 1, // Note: caller_get_posts is depreciated
        'orderby' => 'title',
        'no_found_rows' => true, // Skip pagination, makes the query faster
        'tax_query' => [
            [
                'taxonomy' => 'category',
                'terms' => $unique_array,
                'include_children' => false,
            ],
        ],
    ];
    $q = new WP_Query( $args );
    return $q;
}

You can then use the code as follows in your single post page

$q = get_related_category_posts();
if ( $q->have_posts() ) {
    while ( $q->have_posts() ) {
    $q->the_post();

        // Your loop

    }
    wp_reset_postdata();
}