wp-related-posts.php

function get_related_posts($post, $post_type = 'post', $taxonomy = 'tag', $max_posts = null) {
		# Cache terms for this post and taxonomy
		$terms = wp_cache_get( $post->ID . 'terms_for_' . $taxonomy );
		if ( false === $terms ) {
			$terms = get_the_terms($post->ID , $taxonomy);
			wp_cache_set( $post->ID . 'terms_for_' . $taxonomy, $terms );
		}
		
		$term_ids = array();
		$result = array();
		
		# If max_posts isn't provided, fall back to global posts_per_page option
		if ($max_posts == null) {
			$max_posts = get_option('posts_per_page');
		}
		
		# Map array of term ojects to an array of term ID's
		if (!empty($terms)) foreach ($terms as $term) {
			array_push($term_ids, $term->term_id);
		}
		
		if (!empty($term_ids)) {
			$related_posts = new WP_Query(array(
				'post_type' => $post_type,
				'posts_per_page' => $max_posts,
				'post__not_in' => array($post->ID),
				'tax_query' => array(array(
					'taxonomy' => $taxonomy,
					'field' => 'id',
					'terms' => $term_ids
				))
			));
			
			if($related_posts->have_posts()) {
				foreach ($related_posts->posts as $related_post) {
					array_push($result, $related_post);
				}
			}
		}
		
		return $result;
	}