How to get next and previous post links, alphabetically by title, across post types, in a shortcode

Question

So in order to do this, I had to filter the SQL queries. I found this snippet that filters post order by title and returns them for next and previous post links. Unfortunately, this doesn’t work in a custom post type. So I replaced ‘post’ with get_post_type($post) to grab the current post type and return it. This then allows this to work in custom post types. AND, if you wanted to, you could limit this so that it ONLY works in custom post types, and not blog posts. I didn’t do that here, but it’s possible. Here’s the code I put in my functions.php:

function filter_next_post_sort($sort) {
    $sort = "ORDER BY p.post_title ASC LIMIT 1";
    return $sort;
}
function filter_next_post_where($where) {
    global $post, $wpdb;
    return $wpdb->prepare("WHERE p.post_title > '%s' AND p.post_type="". get_post_type($post)."" AND p.post_status="publish"",$post->post_title);
}

function filter_previous_post_sort($sort) {
    $sort = "ORDER BY p.post_title DESC LIMIT 1";
    return $sort;
}
function filter_previous_post_where($where) {
    global $post, $wpdb;
    return $wpdb->prepare("WHERE p.post_title < '%s' AND p.post_type="". get_post_type($post)."" AND p.post_status="publish"",$post->post_title);
}

add_filter('get_next_post_sort',   'filter_next_post_sort');
add_filter('get_next_post_where',  'filter_next_post_where');

add_filter('get_previous_post_sort',  'filter_previous_post_sort');
add_filter('get_previous_post_where', 'filter_previous_post_where');

Next, I set up a couple shortcodes to be able to add the next and previous post links. Because the theme I’m using gets screwy if there’s nothing returned (and the first and last post won’t return anything for the previous and next post link, respectively), I needed to return a blank space:

function next_shortcode($atts) {
    global $post;
    ob_start(); 
    next_post_link( '<div class="nav-next">%link</div>', 'Next Work <span class="arrow_carrot-right_alt2"></span>' );              
    $result = ob_get_contents();
    ob_end_clean();
    $result = (!$result ? '<div class="nav-next">&nbsp;</div>' : $result);
    return $result;
}

function prev_shortcode($atts) {
    global $post;
    ob_start();
    previous_post_link( '<div class="nav-previous">%link</div>', '<span class="arrow_carrot-left_alt2"></span> Previous Work' );              
    $result = ob_get_contents();
    ob_end_clean();
    $result = (!$result ? '<div class="nav-previous">&nbsp;</div>' : $result);
    return $result;
}
add_shortcode( 'prev_work', 'prev_shortcode' );
add_shortcode( 'next_work', 'next_shortcode' );

Note that I’m using Elegant Themes’ elegant icon font, so that’s what the <span> with the arrow_carrot-left/right_alt2 class is for.

Anyway, hope this helps someone else!!

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