Pages don’t work with custom permalinks and categories

My permalink is set to Custom: /%category%/%post_id%, using WP 2.7.1 with the WordPress Default theme.

The problem occurs when you have several pages of posts. The first page will display fine, but if you try to go to another page (clicking on Older Entrie) you get a 404 error.

Example:
When I go to a category page (let’s call it ‘stuff’) like https://www.mysite.com/wordpress/stuff it correctly shows the posts for the first page of the category, and if you hover over the Older Entries links is says https://www.mysite.com/wordpress/stuff/page/2
but if you click on this link, you get a 404 Error, and you cannot get to the other pages.

Solution:
In the particular case above, $query_string contains ‘category_name’=’stuff/page’ and also contains ‘p’=’2’. The plugin below removes the ‘/page’ from the ‘category_name’, unsets the ‘p’ variable, and sets ‘paged’=’2’. This appears to solve my problem.

I initially noticed the problem while trying to use the wp-pagenavi plugin, but the problem even existed in the default theme with the plugin deactiviated, so it must a wordpress bug. The above solution solved my problem with the default them and also works with wp-pagenavi.

PLUGIN CODE
———–

<?php
/*
Plugin Name: Fix Paging in Category Listings
Plugin URI:
Description: Fixes a bug where next/previous page links are broken in category listings
Version: 0.6
Author: Doug Smith (modified by Jeff Sherk)
Author URI:

Modified on March 23, 2009 by Jeff Sherk for WordPress 2.7.1

Based on original plugin info listed below:
Plugin Name:  Fix Paging in Category Listings
Plugin URI: https://www.thinkbarefoot.com
Description: Fixes a bug where next/previous links are broken in category by year/month listings
Version: 0.5
Author: Doug Smith
Author URI: https://www.thinkbarefoot.com

Copyright 2007  Doug Smith  (email: [email protected])

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

*/

/**
 * Function to fix problem where next/previous buttons are broken on list
 * of posts in a category when the custom permalink string is:
 * /%category%/%year%/%monthnum%/%postname%/
 * The problem is that with a url like this:
 *
 * /category/2007/10/page/2
 *
 * the 'page' looks like a post name, not the keyword "page"
 *
 * MODIFIED ON March 23, 2009 by Jeff Sherk
 *  Permalink structure was /%category%/%post_id% which looked like
 *   www.mysite.com/wordpress/news/27
 *  When attempting to go to another page, it looked like this
 *   www.mysite.com/wordpress/news/27/page/2
 *  but would generate a 404 error .
 *
 *  This modification takes $query_string['category_name'] and chops the '/page'
 *  off the end. It also takes $query_string['paged'] and sets it equal to
 *  $query_string['p'], and then unsets $query_string['p'].
 *  'p' is not needed, but 'paged' is needed in order to make it work correctly
 */
function fix_page_in_category_from_query_string($query_string) { 

    //Check to see if the 'p' and 'category_name' are set in $query_string
    if ( isset($query_string['category_name']) &&  isset($query_string['p']) ) {

      $category_name = $query_string['category_name'];
      $category_len = strlen($category_name); 

      //Check to see if the 'category_name' has '/page' on the end of it
      if (substr($category_name, $category_len-5,5) == '/page') {

        //Remove '/page' from the end of 'category_name'
        $query_string['category_name'] = substr($query_string['category_name'],0,$category_len-5);

        //Set 'paged' equal to the page you want to go to
        $query_string['paged'] = $query_string['p'];

        //Unset 'p' since we don't need it anymore because we set 'paged' instead
        unset($query_string['p']);
      }
    }
    return $query_string;
}

add_filter('request', 'fix_page_in_category_from_query_string');

?>