Archives by Category

snippet.php

<?php 
/*
Plugin Name: Archives for a category 
Plugin URI: http://kwebble.com/blog/2007_08_15/archives_for_a_category
Description: Adds a cat parameter to wp_get_archives() to limit the posts used to generate the archive links to one or more categories.   
Author: Rob Schlüter
Author URI: http://kwebble.com/
Version: 1.4b

Copyright
=========
Copyright 2007, 2008, 2009 Rob Schlüter. All rights reserved.

Licensing terms
===============
- You may use, change and redistribute this software provided the copyright notice above is included. 
- This software is provided without warranty, you use it at your own risk. 

Installation
============
1. Put the kwebble_archives_by_cat.php file in your WordPress plugin directory, <your wordpress dir>/wp-content/plugins.
2. Activate the plugin 'Archives for a category' on the Plugin Management page of the WordPress administration panel.
3. Optionally disable the canonical URLs from the menu Settings | Kwebble.

Usage
=====
After installing and activating the plugin the wp_get_archives() function accepts a 'cat' 
parameter to specify the categories of posts to show in the list of archives. The value of the 
'cat' parameter must be a list of one or more category ID's, separated by comma's. 

If you specify the value of a category ID the posts from that category will be used to create the 
list of archives. If you place a minus sign '-' in front of an ID the posts from that category 
will be excluded.

Depending on the number of categories, your use of them and selection of categories to inlcude in 
the archive list it may be easier to specify all categories to include or just those to exclude.  

You need to make sure the template used to show each archive displays posts from the selected 
category. I'm using category specific templates on this site, like category-id where id is the ID 
of the category to display.
You can use other templates in the template hierarchy, but make sure the template shows items of 
the categories you specify.

At some WordPress version the categories ID's are no longer visible on the admin pages. You can 
find the ID of a category by opening the page to edit the category and inspect the URL of that 
page. The value after cat_ID= is the ID of the category.

Examples
========
Show the default monthly list of archives for category 1:
<?php wp_get_archives('cat=1'); ?>

The same list, but with posts from categories 1 and 3:
<?php wp_get_archives('cat=1,3'); ?>

Use posts from all categories except category 2:
<?php wp_get_archives('cat=-2'); ?>

Use posts from all categories except categories 2 and 8:
<?php wp_get_archives('cat=-2,-8'); ?>

Create a list of archives for category 1 as a dropdown box use:
<?php wp_get_archives('format=option&cat=1'); ?>

For a complete description of all other parameters see the documentation of wp_get_archives().

Limitations
===========
This plugin does not work for weekly archives. The list with archive links is correct, but the 
links themselves do not include the category. So when used, WordPress will not filter the resulting 
page on the category.
The technical reason is that WordPress does not apply filters when the links for weekly archives 
are generated, so the plugin can't change them. Perhaps this is fixed in a next version of 
WordPress.

A WordPress feature added in version 2.3, called canonical URLs, redirects browsers on certain 
URLs. This also happens with the URLs for the archives with a cat parameter. This causes the 
archive pages to contain posts which do not belong to the selected period.

To solve this problem the plugin can disable canonical URLs. Go to the administration section of 
your blog, select Settings and the Kwebble option. On that page you will find a setting to disable 
canonical URLs. This is done using the same technique described in the 
<a href="http://txfx.net/files/wordpress/disable-canonical-redirects.phps">Disable Canonical URL Redirection plugin</a> 
Mark Jaquith made.

This plug-in was developed and tested to work correctly with WordPress versions 2.7.1, but it 
probably works with earlier versions back to 2.3.

History
=======
1.0
- Initial version, works with WordPress 2.2.1.

1.2
- Added support for WordPress 2.3.1.

1.3
- Added support for multiple categories.

1.4
- Categories can be excluded.

1.4a (bugfix)
- Corrected post count when posts belong to multiple categories.
- SQL queries now respect the configured SQL table prefix.
- Templates with multiple calls to wp_get_archives(), with and without 'cat' parameter, generate correct URL's.

1.4b (bugfix)
- Solved the bug where only the first link of an archive list included a selection by category and all other didn't. This also removes the possibility to use multiple calls to wp_get_archives(), with and without 'cat' parameter.
*/

/**
 * Changes the WHERE clause for wp_get_archives to select only posts for the categories in the
 * 'cat' parameter.
 *
 * @param String $where
 *             a SQL WHERE clause.
 * @param Array $args
 *             arguments passed to the wp_get_archives() function.
 *
 * @return String
 *             modified SQL WHERE clause with additional selection by category if $args contains a
 *             parameter called cat.
 */
function kwebble_getarchives_where_for_category($where, $args){
	global $kwebble_getarchives_data, $wpdb;

	if (isset($args['cat'])){
		// Preserve the category for later use.
		$kwebble_getarchives_data['cat'] = $args['cat'];

		// Split 'cat' parameter in categories to include and exclude.
		$allCategories = explode(',', $args['cat']);

		// Element 0 = included, 1 = excluded.
		$categories = array(array(), array());
		foreach ($allCategories as $cat) {
			if (strpos($cat, ' ') !== FALSE) {
				// Multi category selection.
			}
			$idx = $cat < 0 ? 1 : 0;
			$categories[$idx][] = abs($cat);
		}

		$includedCatgories = implode(',', $categories[0]);
		$excludedCatgories = implode(',', $categories[1]);

		// Add SQL to perform selection.
		if (get_bloginfo('version') < 2.3){
			$where .= " AND $wpdb->posts.ID IN (SELECT DISTINCT ID FROM $wpdb->posts JOIN $wpdb->post2cat post2cat ON post2cat.post_id=ID";

			if (!empty($includedCatgories)) {
				$where .= " AND post2cat.category_id IN ($includedCatgories)";
			}
			if (!empty($excludedCatgories)) {
				$where .= " AND post2cat.category_id NOT IN ($excludedCatgories)";
			}

			$where .= ')';
		} else{
			$where .= ' AND ' . $wpdb->prefix . 'posts.ID IN (SELECT DISTINCT ID FROM ' . $wpdb->prefix . 'posts'
					. ' JOIN ' . $wpdb->prefix . 'term_relationships term_relationships ON term_relationships.object_id = ' . $wpdb->prefix . 'posts.ID'
					. ' JOIN ' . $wpdb->prefix . 'term_taxonomy term_taxonomy ON term_taxonomy.term_taxonomy_id = term_relationships.term_taxonomy_id'
					. ' WHERE term_taxonomy.taxonomy = \'category\'';
			if (!empty($includedCatgories)) {
				$where .= " AND term_taxonomy.term_id IN ($includedCatgories)";
			}
			if (!empty($excludedCatgories)) {
				$where .= " AND term_taxonomy.term_id NOT IN ($excludedCatgories)";
			}

			$where .= ')';
		}
	}

	return $where;
}

/**
 * Changes the archive link to include the categories from the 'cat' parameter.
 * 
 * @param String
 *             $url the generated URL for an archive.
 *
 * @return String
 *             modified URL that includes the category.
 */
function kwebble_archive_link_for_category($url){
	global $kwebble_getarchives_data;

	if (isset($kwebble_getarchives_data['cat'])){
		$url .= strpos($url, '?') === false ? '?' : '&';
		$url .= 'cat=' . $kwebble_getarchives_data['cat'];
	}

	return $url;
}

/*
 * Add the filters.
 */

// Prevent error if executed outside WordPress.
if (function_exists('add_filter')){
	// Constants for form field and options.
	define('KWEBBLE_OPTION_DISABLE_CANONICAL_URLS', 'kwebble_disable_canonical_urls');
	define('KWEBBLE_GETARCHIVES_FORM_CANONICAL_URLS', 'kwebble_disable_canonical_urls');
	define('KWEBBLE_ENABLED', '');
	define('KWEBBLE_DISABLED', 'Y');

	add_filter('getarchives_where', 'kwebble_getarchives_where_for_category', 10, 2);

	add_filter('year_link', 'kwebble_archive_link_for_category');
	add_filter('month_link', 'kwebble_archive_link_for_category');
	add_filter('day_link', 'kwebble_archive_link_for_category');

	// Disable canonical URLs if the option is set.
	if (get_option(KWEBBLE_OPTION_DISABLE_CANONICAL_URLS) == KWEBBLE_DISABLED){
		remove_filter('template_redirect', 'redirect_canonical');
	}
}

/*
 * Option settings.
 */

// Hook for adding admin menu.
add_action('admin_menu', 'kwebble_getarchives_admin_pages');

// Action function for above hook.
function kwebble_getarchives_admin_pages() {
	// Add a new submenu under Options:
	add_options_page('Kwebble', 'Kwebble', 'manage_options', 'kwebble_options', 'kwebble_getarchives_admin_options_page');
}

/*
 * Shows the admininstration form with the plugin settings.
 */
function kwebble_getarchives_admin_options_page() {
	$value = get_option(KWEBBLE_OPTION_DISABLE_CANONICAL_URLS);
	$kwebble_disable_canonical_urls = $value === false ? KWEBBLE_ENABLED : $value;
	$checked = $kwebble_disable_canonical_urls == KWEBBLE_DISABLED ? ' checked="checked"' : '';
	?>

	<div class="wrap">
		<h2>Kwebble get_archives with category</h2>
		<form method="post" action="options.php">
			<p class="submit">
				<input type="submit" name="Submit" value="<?php _e('Update Options &raquo;') ?>" />
			</p>

			<p>
				<?php wp_nonce_field('update-options') ?>
				<input type="hidden" name="action" value="update" />
				<input type="hidden" name="page_options" value="<?php echo KWEBBLE_GETARCHIVES_FORM_CANONICAL_URLS; ?>" />

				The <a href="http://markjaquith.wordpress.com/2007/09/25/wordpress-23-canonical-urls/">canonical URLs</a>
				feature introduced with WordPress version 2.3, may interfere with this plugin. If that happens the archive
				pages contain posts outside the archive period. To solve this problem you can disable canonical URLs.<br/>
			</p>

			<p>
				<label><input type="checkbox" name="<?php echo KWEBBLE_GETARCHIVES_FORM_CANONICAL_URLS; ?>" value="<?php echo KWEBBLE_DISABLED; ?>" <?php echo $checked; ?> /> Disable canonical URLs.</label>
			</p>

			<p class="submit">
				<input type="submit" name="Submit" value="<?php _e('Update Options &raquo;') ?>" />
			</p>
		</form>
	</div>

	<?php
}
?>

it works with the current wp version 4.X ?