Can the Next/Prev Post links be ordered by menu order or by a meta key?

wordpress.stackexchange https://wordpress.stackexchange.com/questions/357858

Question

I have a series of posts that are ordered by a meta_key value. They could also be arranged by menu order, if necessary.

The next/prev post links (generated by next_post_link, previous_post_link, or posts_nav_link all navigate by chronology. While I understand this default behaviour, I don't understand how to change it. I found that it maps through to adjacent_post_link in link-template.php, but then it starts to seem fairly hard-coded. Is it recommended to re-write this from scratch to replace it, or is there a better solution.

Was it helpful?

Solution

Understanding the internals

The "sort" order of adjacent (next/prev) posts is not really a sort "order". It's a separate query on each request/page, but it sorts the query by the post_date - or the post parent if you have a hierarchical post as currently displayed object.

When you take a look at the internals of next_post_link(), then you see that it's basically an API wrapper for adjacent_post_link(). The later function calls get_adjacent_post() internally with the $previous argument/flag set to bool(true|false) to grab the next or previous post link.

What to filter?

After digging deeper into it, you'll see that get_adjacent_post() Source link has some nice filters for its output (a.k.a. query result): (Filter Name/Arguments)

  • "get_{$adjacent}_post_join"

    $join
// Only if `$in_same_cat`
// or: ! empty( $excluded_categories` 
// and then: 
// " INNER JOIN $wpdb->term_relationships AS tr 
//     ON p.ID = tr.object_id 
// INNER JOIN $wpdb->term_taxonomy tt 
//     ON tr.term_taxonomy_id = tt.term_taxonomy_id"; 
// and if $in_same_cat then it APPENDS: 
// " AND tt.taxonomy = 'category' 
// AND tt.term_id IN (" . implode(',', $cat_array) . ")";
$in_same_cat
$excluded_categories

  • "get_{$adjacent}_post_where"

    $wpdb->prepare(
      // $op = $previous ? '<' : '>'; | $current_post_date
       "WHERE p.post_date $op %s "
      // $post->post_type
      ."AND p.post_type = %s "
      // $posts_in_ex_cats_sql = " AND tt.taxonomy = 'category' 
      // AND tt.term_id NOT IN (" . implode($excluded_categories, ',') . ')'; 
      // OR empty string if $in_same_cat || ! empty( $excluded_categories
      ."AND p.post_status = 'publish' $posts_in_ex_cats_sql "
    ",
    $current_post_date,
    $post->post_type
)
$in_same_cat
$excluded_categories

  • "get_{$adjacent}_post_sort"

    "ORDER BY p.post_date $order LIMIT 1"`

So you can do alot with it. That starts with filtering the WHERE clause, as well as the JOINed table and the ORDER BY statement.

The result gets cached in memory for the current request, so it doesn't add additional queries if you call that function multiple times on a single page.

Automatic query building

As @StephenHarris pointed out in the comments, there's a core function that might come in handy when building the SQL Query: get_meta_sql() - Examples in Codex. Basically this function is just used to build the meta SQL statement that gets used in WP_Query, but you can use it in this case (or others) as well. The argument that you throw into it is an array, the exact same that would add to a WP_Query.

$meta_sql = get_meta_sql(
    $meta_query,
    'post',
    $wpdb->posts,
    'ID'
);

The return value is an array:

$sql => (array) 'join' => array(),
        (array) 'where' => array()

So you can use $sql['join'] and $sql['where'] in your callback.

Dependencies to keep in mind

In your case the easiest thing would be to intercept it in a small (mu)plugin or in your themes functions.php file and alter it depending on the $adjacent = $previous ? 'previous' : 'next'; variable and the $order = $previous ? 'DESC' : 'ASC'; variable:

The actual filter names

So the filter names are:

  • get_previous_post_join, get_next_post_join
  • get_previous_post_where, get_next_post_where
  • get_previous_post_sort, get_next_post_sort

Wrapped up as a plugin

...and the filter callback would be (for example) something like the following:

<?php
/** Plugin Name: (#73190) Alter adjacent post link sort order */
function wpse73190_adjacent_post_sort( $orderby )
{
    return "ORDER BY p.menu_order DESC LIMIT 1";
}
add_filter( 'get_previous_post_sort', 'wpse73190_adjacent_post_sort' );
add_filter( 'get_next_post_sort', 'wpse73190_adjacent_post_sort' );

OTHER TIPS

Kaiser's answer is awesome and thorough, however just changing the ORDER BY clause isn't enough unless your menu_order matches your chronological order.

I can't take credit for this, but I found the following code in this gist:

<?php
/**
 * Customize Adjacent Post Link Order
 */
function wpse73190_gist_adjacent_post_where($sql) {
  if ( !is_main_query() || !is_singular() )
    return $sql;

  $the_post = get_post( get_the_ID() );
  $patterns = array();
  $patterns[] = '/post_date/';
  $patterns[] = '/\'[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}\'/';
  $replacements = array();
  $replacements[] = 'menu_order';
  $replacements[] = $the_post->menu_order;
  return preg_replace( $patterns, $replacements, $sql );
}
add_filter( 'get_next_post_where', 'wpse73190_gist_adjacent_post_where' );
add_filter( 'get_previous_post_where', 'wpse73190_gist_adjacent_post_where' );

function wpse73190_gist_adjacent_post_sort($sql) {
  if ( !is_main_query() || !is_singular() )
    return $sql;

  $pattern = '/post_date/';
  $replacement = 'menu_order';
  return preg_replace( $pattern, $replacement, $sql );
}
add_filter( 'get_next_post_sort', 'wpse73190_gist_adjacent_post_sort' );
add_filter( 'get_previous_post_sort', 'wpse73190_gist_adjacent_post_sort' );

I've modified the function names for WP.SE.

If you only change the ORDER BY clause, the query still looks for posts greater than or less than the current post date. If your posts aren't in chronological order, you won't get the right post.

This changes the where clause to look for posts where the menu_order is greater than or less than the current post's menu_order, in addition to modifying the orderby clause.

The orderby clause also shouldn't be hardcoded to use DESC as it will need to switch based on whether you are getting the next or previous post link.

Tried to hook in without success. Might be just a problem of my configuration, but for those who can't make the hook work, here is the simplest solution:

<?php
    $all_posts = new WP_Query(array(
        'orderby' => 'menu_order',
        'order' => 'ASC',
        'posts_per_page' => -1
    ));

    foreach($all_posts->posts as $key => $value) {
        if($value->ID == $post->ID){
            $nextID = $all_posts->posts[$key + 1]->ID;
            $prevID = $all_posts->posts[$key - 1]->ID;
            break;
        }
    }
?>
<?php if($prevID): ?>
    <span class="prev">
        <a href="<?= get_the_permalink($prevID) ?>" rel="prev"><?= get_the_title($prevID) ?></a>
    </span>
<?php endif; ?>
<?php if($nextID): ?>
    <span class="next">
        <a href="<?= get_the_permalink($nextID) ?>" rel="next"><?= get_the_title($nextID) ?></a>
    </span>
<?php endif; ?>

function wpse73190_gist_adjacent_post_sort( $sql ) {
    $pattern = '/post_date/';
    $replacement = 'menu_order';

    return preg_replace( $pattern, $replacement, $sql );
}

add_filter( 'get_next_post_sort', 'wpse73190_gist_adjacent_post_sort' );
add_filter( 'get_previous_post_sort', 'wpse73190_gist_adjacent_post_sort' );

Based on @Szabolcs Páll's answer I've created this utility class with helper methods to be able to get posts of type by menu order and get the next and previous post by menu order as well. I've additionally added conditions to check if the current post is the first or last post to get the last or first post respectively.

For example:

// $currentPost is first by menu order
getPreviousPostByMenuOrder($postType, $$currentPost->ID)
// returns => last post by menu order

// $currentPost is last by menu order
getPreviousPostByMenuOrder($postType, $$currentPost->ID)
// returns => first post by menu order

The full class:

class PostMenuOrderUtils {

    public static function getPostsByMenuOrder($postType){
        $args =[
            'post_type' => $postType,
            'orderby' => 'menu_order',
            'order' => 'ASC',
            'posts_per_page' => -1
        ];

        $posts = get_posts($args);

        return $posts;
    }

    public static function getNextPostByMenuOrder($postType, $postID){
        $posts = self::getPostsByMenuOrder($postType);

        $nextPost = null;

        foreach($posts as $key => $value) {
            if($value->ID == $postID){
                $nextPost = $posts[$key] !== end($posts) ? $posts[$key + 1] : $posts[0];

                break;
            }
        }

        return $nextPost;
    }

    public static function getPreviousPostByMenuOrder($postType, $postID){
        $posts = self::getPostsByMenuOrder($postType);


        $prevPost = null;

        foreach($posts as $key => $value) {
            if($value->ID == $postID){
                $prevPost = $key !== 0 ? $posts[$key - 1] : end($posts);
                break;
            }
        }

        return $prevPost;
    }

}

I find this small plugin really handy: http://wordpress.org/plugins/wp-query-powered-adjacent-post-link/

WP_Query Powered Adjacent Post Link is a plugin for developers. It adds the function wpqpapl(); to WordPress which can return information on the previous and next post to the current. It accepts arguments for use in the WP_Query class.

This worked for me:

add_filter( 'get_previous_post_where', 'so16495117_mod_adjacent_bis' );
add_filter( 'get_next_post_where', 'so16495117_mod_adjacent_bis' );
function so16495117_mod_adjacent_bis( $where ) {
    global $wpdb;
    return $where . " AND p.ID NOT IN ( SELECT post_id FROM $wpdb->postmeta WHERE ($wpdb->postmeta.post_id = p.ID ) AND $wpdb->postmeta.meta_key = 'archive' AND $wpdb->postmeta.meta_value = 1 )";
}

Taken from: https://stackoverflow.com/questions/16495117/how-to-skip-certain-links-on-adjacent-posts-in-wordpress

I had issues with this too. I magically got it to work like this:

And i didn't have to write a word of code myself :)

Based on @Szabolcs Páll's answer and bbloomer's post on adding next/prev buttons in WooCommerce Single Product Page, I created this code.

It sorts all products by meta key and adding prev/next buttons above + below the product.

(The meta key can be an ACF field too!)

/**
 * @snippet       Add next/prev buttons sorted by meta key or ACF field @ WooCommerce Single Product Page
 * @testedwith    WooCommerce 4.8.0
 * @source        Elron : https://wordpress.stackexchange.com/a/365334/98773
 * @thanks        bbloomer : https://businessbloomer.com/?p=20567
 * @thanks        Szabolcs Páll : https://wordpress.stackexchange.com/a/284045/98773
 */

add_action('woocommerce_before_single_product', 'elron_prev_next_product');

// and if you also want them at the bottom...
add_action('woocommerce_after_single_product', 'elron_prev_next_product');

function elron_prev_next_product()
{
   global $post;

   echo '<div class="prev-next-buttons">';

   $all_posts = new WP_Query(
      array(
         'post_type' => 'product',
         'meta_key' => 'the_meta_key_or_acf_field', // <-- CHANGE THIS
         'orderby' => 'meta_value',
         'order' => 'DESC',
         'posts_per_page' => -1
      )
   );

   foreach ($all_posts->posts as $key => $value) {
      if ($value->ID == $post->ID) {
         $nextID = $all_posts->posts[$key + 1]->ID;
         $prevID = $all_posts->posts[$key - 1]->ID;
         break;
      }
   }

   if ($prevID) : ?>
      <a href="<?= get_the_permalink($prevID) ?>" rel="prev" class="prev" title="<?= get_the_title($prevID) ?>"><?= esc_attr__('Previous product') ?></a>
   <?php endif; ?>
   <?php if ($nextID) : ?>
      <a href="<?= get_the_permalink($nextID) ?>" rel="next" class="next" title="<?= get_the_title($nextID) ?>"><?= esc_attr__('Next product') ?></a>
   <?php endif; ?>
<?php

   echo '</div>';
}

If you want the extra scss file I used: _prev-next-buttons.scss

.prev-next-buttons {
    background: $lightpurple;
    padding: 2em;
    text-align: center;

    a {
        opacity: 0.7;
        border-radius: 0.5em;
        border: $white 1px solid;
        color: $white;
        display: inline-block;
        padding: 0.5em 0.8em;
        text-decoration: none;
        margin: 0 0.1em;
        &:hover, &:focus {
            opacity: 1;
        }
    }

    .prev {
        &:before {
            content: " 🠔 ";
        }
    }
    .next {
        &:after {
            content: " 🠖 ";
        }
    }
}

.rtl {
    .prev-next-buttons {
        .prev {
            &:before {
                content: " 🠖 ";
            }
        }
        .next {
            &:after {
                content: " 🠔 ";
            }
        }
    }
}

I have found a much easier way to achieve a meta-key based post navigation, without the need to modify functions.php.

My example: You have a products.php and you want to switch between products. The previous product is the next cheaper one, the next product the next more expensive one.

Here comes my solution for single.php:

<div class="post_navigation">

<?php

// Prepare loop
$args = (
'post_type' => 'products',
'post_status' => 'publish',
'meta_key' => 'price',
'orderby' => 'meta_value_num',
'order' => 'ASC',
'posts_per_page' => -1
);
query_posts($args);

// Initialize array in which the IDs of ALL products posts will be stored
$posts = array();

// ... and now let's start the loop
while ( have_posts() ) : the_post();
$posts[] += $post->ID;
endwhile;

// Reset Query
wp_reset_query();

// Identify the position of the current product within the $posts-array 
$current = array_search(get_the_ID(), $posts);

// Identify ID of previous product
$prevID = $posts[$current-1];

// Identify ID of next product
$nextID = $posts[$current+1];

// Link "previous product"
if (!empty($prevID)) { ?>
<a href="/?p=<?php echo $prevID; ?>">previous product</a>
<?php }
// Link "next product"
if (!empty($nextID)) { ?>
<a href="/?p=<?php echo $nextID; ?>">next product</a>

<?php } ?>
Licensed under: CC-BY-SA with attribution
Not affiliated with wordpress.stackexchange
scroll top