Howto: Add Related Topics without a plug-in

I have been busy trying to create a new layout for my website and I want to incorporate related topics without having to rely on a plug-in. I found this tip on how to add related topics using tags.  I have encountered a lot of problems when using query_post() or new WP_Query() inside the loop. It seems that the the_ID somehow always screws up. Also, from that code, it only searches for posts from the first tag and only works in single pages. I wanted to show posts from all of the tags added in my post.

My solution was to create a function and get all the post related to each of the tags; limiting them to 5 post per tag.

Add this inside the function.php in your theme:

1. function getRelatedPost($postID) {
2. global $wpdb;
3. $tags = wp_get_post_tags($postID);
4. $output = ”;
5. //gets all of the tag in a particular post
6. foreach ($tags as $terms) {
7. $first_tag = $terms->term_taxonomy_id;
8. $name = $terms->name;
9. // mysql query joining wp_post and wp_term_relationships
10. $args = “SELECT p.*
11. FROM wp_posts p, wp_term_relationships tr
12. WHERE p.id = tr.object_id
13. AND tr.term_taxonomy_id = $first_tag
14. AND EXISTS( SELECT *
15. FROM wp_term_taxonomy tt
16. WHERE tt.term_taxonomy_id = tr.term_taxonomy_id
17. AND tt.taxonomy = ‘post_tag’
18. )
19. ORDER BY p.post_date DESC LIMIT 0, 5″; // limits 5 post on each tag
20. $myposts = $wpdb->get_results($args);
21. if ($myposts) {
22. foreach($myposts as $post) {
23. // to eliminate double post
24. if ($postID != $post->ID) {
25. $permalink = get_permalink($post->ID);
26. $post_title = stripslashes($post->post_title);
27. $output .= ”<li><a href=”‘ . $permalink . ‘” rel=”bookmark” title=”[ '. $name . '] ‘ . htmlspecialchars($post_title, ENT_COMPAT) . ‘”>’ . htmlspecialchars($post_title). ‘</a></li>’; // creates a list
28. }
29. }
30. }
31. }
32. if ($output) {
33. //creates html list if there is any result;
34. echo ‘<div id=”rellinks” class=”padd”><h5>Related Links:</h5><ul>’;
35. echo $output;
36. echo ‘</ul></div>’;
37. }
38. }

Now that you’ve added this function, use this code anywhere inside or outside the loop:

<?php getRelatedPost($post->ID);  ?>

You can also customize the CSS using the #related-links.

I already incorporated this function on my current theme. To see a working example just look bellow. It gets a little messy if you have a lot of tags. Also, this code isn’t perfect; if you have any suggestions, please feel free to comment.

Anyway, enjoy.

---