In Brad Schiff’s Learn WordPress Udemy course there a few chapters that go over the WP Custom Query. These include “Section 6 – Chapter 24,” “Section 6 – Chapter 41,” and “Section 15 – Chapter 76.”

What is a normal/standard/default query?

WP knows how to query the database for a page or post or blog page. A custom query is where you tell WordPress the exact content you want to query, allowing you to load whatever you want, wherever you want.

A simple “while loop” queries for us by default:

<?php
  while (have_posts()) {
    the_post(); ?>
    <li><?php the_title(); ?></li>
  <?php }
?>

Whenever you begin writing a custom query you begin by creating a variable that creates a new instance of a “WP_Query” object. In the “while loop,” look inside of that variable:

<?php
  $homepagePosts = new WP_Query(array(
     // check out all available parameters in docs
    'posts_per_page' => 2,
    'category_name' => 'awards'
  ));
  
  while ($homepagePosts->have_posts()) {
    $homepagePosts->the_post(); ?>
    <li><?php the_title(); ?></li>
  <?php }
?>

We wouldn’t want to hard-code the category name since we want it to be whatever the category for the current post is. We can probably just create and reference a variable.

// Something like this?
// Couldn't get to work
$current_category = wp_get_post_terms( get_the_ID(), 'category' );

Querying can be an expensive operation so you want to consider refactoring your code to make it as efficient as possible.

I ended up copying the snippet below from this website

<div><?php
    $rand_same_cat_args = array(
        'post_type' => 'post',
        'post_status' => 'publish',
        'orderby' => 'rand',
        'posts_per_page' => '1', // get 5 posts
        'ignore_sticky_posts' => 1,
    );

    // This code snippet pasted in from
    // https://www.wpexplorer.com/related-posts-category/
    // Check for current post category and add tax_query to the query arguments
    $cats = wp_get_post_terms( get_the_ID(), 'category' ); 
    $cats_ids = array();  
    foreach( $cats as $wp_ecp_related_cat ) {
        $cats_ids[] = $wp_ecp_related_cat->term_id; 
    }
    if ( ! empty( $cats_ids ) ) {
        $rand_same_cat_args['category__in'] = $cats_ids;
    }

    // back to my code that runs custom query of posts
    $my_query_rand_same_cat = new WP_Query( $rand_same_cat_args );

    // loop through posts for custom query
    if ( $my_query_rand_same_cat->have_posts() ) :

        while ( $my_query_rand_same_cat->have_posts() ) : $my_query_rand_same_cat->the_post();
            // display article
            ?>
            <div class="btn--centered"><a href="<?php the_permalink()?>">Random From Same Category<a></div>
            <?php
        endwhile;
    endif;
    wp_reset_postdata();
?>
    </div>

Note the use of ‘category__in’ instead of ‘category_name’ as a key in the array.