WordPress noodling: displaying date-based archives from only one category

I have a client who’s using the Posts functions in Wordpress for multiple purposes. One issue we’ve run up against is that we want the date-based archives (i.e., in the sidebar, showing the months of posts) to only pull from one category out of the 30-40 categories that they have. I was using wp_get_archives, but it doesn’t have a category parameter as I’d hoped.

After some futzing around, I found a combo of two solutions that worked. Here’s the code I dropped into my theme’s functions.php; then I used wp_get_archives in another function to create a widget for the sidebar (not included below). Enjoy!

## First, on monthly archives, only display posts from the category with an ID of 109
function exclude_stuff($query) {
    if ( $query->is_month) {
        $query->set(‘cat’, ‘109’);
        }
    return $query;
    }
add_filter(‘pre_get_posts’, ‘exclude_stuff’);


## Then, when wp_get_archives is used to display monthly archives, only show months with posts from the category with an ID of 109
add_filter( ‘getarchives_where’, ‘customarchives_where’ );
add_filter( ‘getarchives_join’, ‘customarchives_join’ );

function customarchives_join( $x ) {
    global $wpdb;
    return $x . ” INNER JOIN $wpdb->term_relationships ON ($wpdb->posts.ID = $wpdb->term_relationships.object_id) INNER JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)”;

}

function customarchives_where( $x ) {
    global $wpdb;
    $includes= ‘109’; // category id to include
    return $x . ” AND $wpdb->term_taxonomy.taxonomy = ‘category’ AND $wpdb->term_taxonomy.term_id = ‘$includes’”;
}