{"id":141,"date":"2005-11-01T14:39:30","date_gmt":"2005-11-01T19:39:30","guid":{"rendered":"http:\/\/ronrothman.com\/public\/leftbraned\/?p=141"},"modified":"2019-02-15T20:56:28","modified_gmt":"2019-02-16T01:56:28","slug":"wordpress-fix-category-exclusions-in-next_post_linkprevious_post_link","status":"publish","type":"post","link":"https:\/\/www.ronrothman.com\/public\/leftbraned\/wordpress-fix-category-exclusions-in-next_post_linkprevious_post_link\/","title":{"rendered":"WordPress: Fix Category Exclusions in next_post_link() \/ previous_post_link()"},"content":{"rendered":"
(UPDATE: Word on the street (see comment 27<\/a>, below) is that this bug has been fixed in WordPress 2.1.)<\/div>\n

I recently came across a known bug in WordPress 1.5.2 (well, at least it’s known<\/a> to users; I can only assume that the dev community is also aware of it). Just wanted to post my fix here, in case anyone else finds it helpful.<\/p>\n

The Bug<\/h3>\n

Category exclusion<\/strong> is broken. The problem is that the category exclusion parameter (the 4th param) of next_post_link()<\/code><\/strong> and previous_post_link()<\/code><\/strong> is effectively ignored.
\n
\n(next_post_link()<\/code> and previous_post_link()<\/code> are the new versions of the now-deprecated next_post()<\/code> and previous_post()<\/code>.)<\/p>\n

A quick scan through the WordPress code indicates that the “category exclude” feature isn’t even implemented (at least not in a serious way) for next\/previous_post_link. I haven’t spent much time perusing the WordPress code base, but from what I can tell, it seems that the relevant sections of these functions were never upgraded from an earlier WP version–one with a different schema; in particular, one with a different method of storing post-category relationships.<\/p>\n

The Fix<\/span>Hack<\/h3>\n

Here is how I fixed it in my installation (see warnings below<\/strong> before trying this at home):<\/p>\n

1. Edit wp-includes\/template-functions-links.php<\/code>. At approximately line 253 (in function get_previous_post<\/code>) [line 221 in WP1.5], you’ll see this:<\/p>\n

    $sql_exclude_cats = '';\n    if (!empty($excluded_categories)) {\n        $blah = explode('and', $excluded_categories);\n        foreach($blah as $category) {\n            $category = intval($category);\n            $sql_exclude_cats .= \" AND post_category != $category\";\n        }\n    }\n<\/pre>\n
2.  Replace that block with the following (beware of copy\/paste errors<\/strong>, especially with respect to line breaks):<\/p>\n
    $sql_exclude_cats = '';\n    if (!empty($excluded_categories)) {\n### ronr hack BEGIN ###\n        # find ids of all posts in excluded cats\n        $query =\n            \"SELECT post_id\n             FROM $wpdb->post2cat\n             WHERE category_id IN (\"\n             . str_replace(',', ',', $excluded_categories)\n             . ')';\n        $excluded_post_rows = $wpdb->get_results($query);\n\n        # build IN clause from those ids\n        if (count($excluded_post_rows) > 0) {\n            $sql_exclude_cats =\n                ' AND ID NOT IN ('\n                . intval($excluded_post_rows[0]->post_id);\n            for ($i = 1; $i < (count($excluded_post_rows)); $i++) {\n                $sql_exclude_cats .=\n                    ','\n                    . intval($excluded_post_rows[$i]->post_id);\n            }\n            $sql_exclude_cats .= \" )\";\n        }\n### ronr hack END ###\n    }\n<\/pre>\n
(Note: instead of copy\/pasting the above code, you can download it here<\/a>.)<\/p>\n
3.  Now, make the same replacement<\/strong> in the corresponding block in get_next_post<\/code>, which is a little further down in the file.<\/p>\n
Disclaimers<\/h3>\n
Presumably, this bug will be fixed properly in an upcoming release, so now that I’ve got it working (albeit jury-rigged), I’m not going to spend any more time on it.  If it doesn’t get fixed soon, perhaps I’ll clean it up and fold it into a plug-in (perhaps even as Asides plug-in).<\/p>\n
My code does no error checking<\/strong>, and it assumes<\/strong> that the value of the exclude_categories parameter is not screwy.  It’s provided as-is.  I would never release code like this if it wasn’t intended to be used solely by me.  If I wrote code like this at work, I’d deserve to be fired.  Constructive suggestions for improvements are always welcome, but please don’t bitch to me about how it didn’t work for you, broke your blog, crashed your server, ruined your marriage, etc.  Capisce?<\/i><\/p>\n
Note too that I’ve changed the original interface; instead of separating excluded category ids with the word “and” (odd), it now expects a comma (not odd).<\/p>\n
Anyway, good luck.  And if you happen to find this useful, please let me know<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
(UPDATE: Word on the street (see comment 27, below) is that this bug has been fixed in WordPress 2.1.) I recently came across a known bug in WordPress 1.5.2 (well, at least it’s known to users; I can only assume that the dev community is also aware of it). Just wanted to post my fix […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0},"categories":[11,5],"tags":[61,54,53],"yoast_head":"\nWordPress: Fix Category Exclusions in next_post_link() \/ previous_post_link() - \u00ableftbraned<\/title>\n<meta name=\"description\" content=\"WordPress: Fix Category Exclusions in next_post_link() \/ previous_post_link()\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ronrothman.com\/public\/leftbraned\/wordpress-fix-category-exclusions-in-next_post_linkprevious_post_link\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"WordPress: Fix Category Exclusions in next_post_link() \/ previous_post_link() - 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