I’m building a catalog site in WordPress for one of my collections. The catalog currently exists in a large Excel spreadsheet and I’ve been usng it to create a CSV file that can be imported using the WP CSV plugin. This greatly speeds up the creation of the content for the catalog. My plan is that each item in my catalog is a post and the CSV file contains all of the information for each post. One of the imported values in the CSV file includes is the post date. I imported each item with an identical post date without giving it too much thought. This is because the catalog site isn’t going to actually display any post dates. Anyway, it turns out that this was a bad idea because the Next Post and Previous Post links in the single.php template will not bring up any of the posts with the same post date. A bit of digging about and I’ve worked out why.

My single.php theme file contains calls to previous_post_link() and next_post_link() which are supposed to render the next/previous links. I drilled down into these functions which can be found in the /wp-includes/link-template.php file. Both functions call the function get_adjecent_post(). Looking at that a bit closer it includes a bunch of SQL criteria code (for selecting posts from the same taxonomy for example) and, as you’d expect it creates a date criteria clause. That bit of php looks like this:

$adjacent = $previous ? 'previous' : 'next';
 $op = $previous ? '<' : '>';
 $order = $previous ? 'DESC' : 'ASC';

Those little ‘<' and '>‘ symbols give the answer why my imported posts with identical post dates don’t display in the next/previous post links. The date criteria to select the next/previous post is “greater than” or “less than” and obviously if the post dates are identical they are NOT greater than or less than. So, the solution is to NOT import posts with identical post dates. Unfortunately I’d already done this so I opened up the wp_posts table in MySQL workbench and edited the post date of each post I’d imported. Next time I do a bulk import I’ll make sure to increment the post date column values in the CSV BEFORE I do the import.