related.php

<?php
/**
 * Related Products
 *
 * This template can be overridden by copying it to yourtheme/woocommerce/single-product/related.php.
 *
 * HOWEVER, on occasion WooCommerce will need to update template files and you
 * (the theme developer) will need to copy the new files to your theme to
 * maintain compatibility. We try to do this as little as possible, but it does
 * happen. When this occurs the version of the template file will be bumped and
 * the readme will list any important changes.
 *
 * @see         https://docs.woocommerce.com/document/template-structure/
 * @author      WooThemes
 * @package     WooCommerce/Templates
 * @version     1.6.4
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

global $product, $woocommerce_loop;

if ( empty( $product ) || ! $product->exists() ) {
    return;
}

if ( ! $related = $product->get_related( $posts_per_page ) ) {
    return;
}

$cats_array = array(0);

// get categories
$terms = wp_get_post_terms( $product->id, 'product_cat' );

// select only the category which doesn't have any children
foreach ( $terms as $term ) {
    $children = get_term_children( $term->term_id, 'product_cat' );
    if ( !sizeof( $children ) )
    $cats_array[] = $term->term_id;
}

var_dump($cats_array);

$args = apply_filters( 'woocommerce_related_products_args', array(
    'post_type' => 'product',
    'ignore_sticky_posts' => 1,
    'no_found_rows' => 1,
    'posts_per_page' => $posts_per_page,
    'orderby' => $orderby,
    'tax_query' => array(
        array(
            'taxonomy' => 'product_cat',
            'field' => 'id',
            'terms' => $cats_array
        ),
    )
));

$products                    = new WP_Query( $args );
$woocommerce_loop['name']    = 'related';
$woocommerce_loop['columns'] = apply_filters( 'woocommerce_related_products_columns', $columns );

if ( $products->have_posts() ) : ?>

    <div class="related products">

        <h2><?php _e( 'Related Products', 'woocommerce' ); ?></h2>

        <?php woocommerce_product_loop_start(); ?>

            <?php while ( $products->have_posts() ) : $products->the_post(); ?>

                <?php wc_get_template_part( 'content', 'product' ); ?>

            <?php endwhile; // end of the loop. ?>

        <?php woocommerce_product_loop_end(); ?>

    </div>

<?php endif;

wp_reset_postdata();