How to display related posts from the same category?

Question

Is it possible to display related posts from same category as the current post?

Answer 1

One possibility:

$related = get_posts( 
    array( 
        'category__in' => wp_get_post_categories( $post->ID ), 
        'numberposts'  => 5, 
        'post__not_in' => array( $post->ID ) 
    ) 
);

if( $related ) { 
    foreach( $related as $post ) {
        setup_postdata($post);
        /*whatever you want to output*/
    }
    wp_reset_postdata();
}

Reference:

• get_posts

• wp_reset_postdata

• wp_get_post_categories

Answer re-written based on WP_Query():

$related = new WP_Query(
    array(
        'category__in'   => wp_get_post_categories( $post->ID ),
        'posts_per_page' => 5,
        'post__not_in'   => array( $post->ID )
    )
);

if( $related->have_posts() ) { 
    while( $related->have_posts() ) { 
        $related->the_post(); 
        /*whatever you want to output*/
    }
    wp_reset_postdata();
}

Answer 2

Here another clean and very flexible option:

Put this code in your functions.php file

function example_cats_related_post() {

    $post_id = get_the_ID();
    $cat_ids = array();
    $categories = get_the_category( $post_id );

    if(!empty($categories) && is_wp_error($categories)):
        foreach ($categories as $category):
            array_push($cat_ids, $category->term_id);
        endforeach;
    endif;

    $current_post_type = get_post_type($post_id);
    $query_args = array( 

        'category__in'   => $cat_ids,
        'post_type'      => $current_post_type,
        'post__not_in'    => array($post_id),
        'posts_per_page'  => '3'


     );

    $related_cats_post = new WP_Query( $query_args );

    if($related_cats_post->have_posts()):
         while($related_cats_post->have_posts()): $related_cats_post->the_post(); ?>
            <ul>
                <li>
                    <a href="<?php the_permalink(); ?>">
                        <?php the_title(); ?>
                    </a>
                    <?php the_content(); ?>
                </li>
            </ul>
        <?php endwhile;

        // Restore original Post Data
        wp_reset_postdata();
     endif;

}

Now you can simply call the function anywhere in your site using:

<?php example_cats_related_post() ?>

You may want to remove the list elements or style them as per your need.

*Edit - you to change this: post_not_in to this post__not_in in your query

Answer 3

you can use this code to get related posts from the same category

$args = array(
                'category__in' => wp_get_post_categories( get_queried_object_id() ),
                'posts_per_page' => 5,
                'orderby'       => 'rand',
                'post__not_in' => array( get_queried_object_id() )
                );
    $the_query = new WP_Query( $args );

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

        <ul class="">
        <!-- the loop -->
        <?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>

            <li>
                <h6>
                    <a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>">
                    <?php the_title(); ?>
                    </a>
                </h6>
            </li>

        <?php endwhile; ?>
        <!-- end of the loop -->
        </ul>

        <?php wp_reset_postdata(); ?>

     <?php endif; ?>

and use this code to get related posts from the same tags

$tags = wp_get_post_terms( get_queried_object_id(), 'post_tag', ['fields' => 'ids'] );
    $args = [
        'post__not_in'        => array( get_queried_object_id() ),
        'posts_per_page'      => 5,
        'orderby'             => 'rand',
        'tax_query' => [
            [
                'taxonomy' => 'post_tag',
                'terms'    => $tags
            ]
        ]
    ];
    $the_query = new WP_Query( $args );
    if ( $the_query->have_posts() ) : ?>

        <ul class="">
        <!-- the loop -->
        <?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>

            <li>
                <h6>
                    <a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>">
                    <?php the_title(); ?>
                    </a>
                </h6>
            </li>

        <?php endwhile; ?>
        <!-- end of the loop -->
        </ul>

        <?php wp_reset_postdata(); ?>

    <?php endif; ?>

Answer 4

This answer makes sure that related posts are ordered by how many tags match.

For example if an article has 3 tags and there is another article that has the exact same 3 tags it should appear at the top of the list. Secondary sorting should be by post date so newer content is favored.

/**
 * Select content with common tags.
 * Sort so content with multiple matching tags are at the top.
 * Secondary sort on most recent content first.
 *
 * @param $post_id
 * @param int $limit
 * @return array
 */
function related_posts($post_id, $limit = 5) {

    global $wpdb;

    $query  = "SELECT TOP %d x.object_id as ID
FROM (
SELECT TOP 10 tr1.object_id, COUNT(tr1.term_taxonomy_id) AS common_tag_count
FROM {$wpdb->term_relationships} AS tr1
INNER JOIN {$wpdb->term_relationships} AS tr2 ON tr1.term_taxonomy_id = tr2.term_taxonomy_id
WHERE tr2.object_id = %d
GROUP BY tr1.object_id
HAVING tr1.object_id != %d
ORDER BY COUNT(tr1.term_taxonomy_id) DESC
) x
INNER JOIN {$wpdb->posts} p ON p.ID = x.object_id
ORDER BY common_tag_count DESC, p.post_date DESC;";

    $query = $wpdb->prepare($query, $limit, $post_id, $post_id);
    $ids = $wpdb->get_col($query);
    $posts = [];
    foreach($ids as $id)  {
        $posts[] = get_post($id);
    }

    return $posts;

}

The inner query here is to select the content with the most matching tags, and then the outer query is just used to to apply secondary sorting by post date.

Note this query is written for SQL Server so some syntax may need updating (e.g. TOP vs LIMIT).