[WordPress] WordPress Pagination: A Simple Utility (And Why)

00-previous-post.php

<?php

global $wpdb;
$results = $wpdb->get_results(
    $wpdb->prepare(
        "
        SELECT *
        FROM $wpdb->posts
        WHERE ID < (
            SELECT ID
            FROM $wpdb->posts
            WHERE ID = %d
            AND post_type = '%s'
            AND post_status = '%s'
            ORDER BY ID DESC
        )
        AND post_type = '%s'
        AND post_status = '%s'
        ORDER BY ID DESC
        LIMIT 1
        ",
        get_the_ID(),
        'acme-custom-post-type',
        'publish',
        'acme-custom-post-type',
        'publish'
    )
);

01-next-post.php

<?php

global $wpdb;
$results = $wpdb->get_results(
    $wpdb->prepare(
        "
        SELECT *
        FROM $wpdb->posts
        WHERE ID > (
            SELECT ID
            FROM $wpdb->posts
            WHERE ID = %d
            AND post_type = '%s'
            AND post_status = '%s'
            ORDER BY ID ASC
        )
        AND post_type = '%s'
        AND post_status = '%s'
        ORDER BY ID ASC
        LIMIT 1
        ",
        get_the_ID(),
        'acme-custom-post-type',
        'publish',
        'acme-custom-post-type',
        'publish'
    )
);

03-has-previous-post.php

<?php 
/**
 * @param array $results the results of the query to determined if there are past posts
 *
 * @return bool true if there is a previous post; otherwise, false
 */
private function hasPreviousPost($results)
{
    return isset($results[0]);
}

04-has-next-post.php

<?php
/**
 * @param array $results the results of the query to determined if there are future posts
 *
 * @return bool true if there is a next post; otherwise, false
 */
private function hasNextPost($results)
{
    return isset($results[0]);
}

05-get-post-link.php

<?php
/**
 * @param array $results the results of the array from which to retrieve the post ID
 *
 * @return string the ID of the post to which we're going to link
 */
private function getPostLink($results)
{
    return get_the_permalink($results[0]->ID);
}