Wordpress: previous_post_link / next_post_link by alphabetical order? - php

Question

I'm developing a wordpress website with custom posts which are ordered alphabetically in the loop.
<!-- THE ARGS -->
<?php global $query_string;
$args = wp_parse_args($query_string);
$args = array(
'post_type' => 'custom_post',
'orderby' => 'title',
'order' => 'ASC',
'posts_per_page' => -1,
); ?>
<!-- THE LOOP -->
<?php $wp_query = new WP_Query( $args ); ?>
<?php while ($wp_query->have_posts()) : $wp_query->the_post(); ?>
<?php endwhile; ?>
<?php wp_reset_query(); ?>
Nothing fancy there, just a normal loop.
When I open a post, in its page I have the usual previous_post_link and next_post_link so I can navigate through posts. However, this is done by chronological order of the posts, and I wish to do so by the same alphabetical order as I used in the loop, of course. Any help on this matter would be very appreciated.
Thanks in advance!

Answer 1

It looks like this plug-in does what you're after, e.g.:
<ul class="pager">
<?php previous_post_link_plus( array('order_by' => 'post_title') ); ?>
<?php next_post_link_plus( array('order_by' => 'post_title') ); ?>
</ul>

Answer 2

You can do this by using filters in the get_adjacent_post function.
In your functions.php file, add:
function mytheme_previous_post_orderby_name($orderby){
return "ORDER BY p.post_title DESC LIMIT 1";
}
function mytheme_previous_post_where_name(){
global $post, $wpdb;
return $wpdb->prepare( "WHERE p.post_title < %s AND p.post_type = %s AND ( p.post_status = 'publish' OR p.post_status = 'private' )", $post->post_title, $post->post_type );
}
function mytheme_next_post_orderby_name($orderby){
return "ORDER BY p.post_title ASC LIMIT 1";
}
function mytheme_next_post_where_name(){
global $post, $wpdb;
return $wpdb->prepare( "WHERE p.post_title > %s AND p.post_type = %s AND ( p.post_status = 'publish' OR p.post_status = 'private' )", $post->post_title, $post->post_type );
}
Then in your single.php page add the filters before you call the previous/next posts link functions:
add_filter('get_previous_post_sort', 'mytheme_previous_post_orderby_name', 10, 1);
add_filter('get_next_post_sort', 'mytheme_next_post_orderby_name', 10, 1);
add_filter('get_previous_post_where', 'mytheme_previous_post_where_name', 10);
add_filter('get_next_post_where', 'mytheme_next_post_where_name', 10);
the_post_navigation();
remove_filter('get_previous_post_sort', 'mytheme_previous_post_orderby_name', 10);
remove_filter('get_next_post_sort', 'mytheme_next_post_orderby_name', 10);
remove_filter('get_previous_post_where', 'mytheme_previous_post_where_name', 10);
remove_filter('get_next_post_where', 'mytheme_next_post_where_name', 10);
If you want to check for your specific post_type, you can add an if around the adding filter section:
if($post->post_type == 'my_custom_post_type'){
add_filter(...);
the_post_navigation();
remove_filter(...);
}
or, you can just use a post_type specific single.php file!
This worked great for me, but there may be some limitations if you are planning on combining this with posts in the same term...