Changing WordPress Query Vars for Specific Archive Pages

When you develop a WordPress theme with multiple custom post types or taxonomies, you’ll inevitably find yourself needing to change some query vars for specific archives. For example, you may want to change the default blog archive from 10 posts to 5, but on the archive page that displays portfolio items, you want to show the most recent 12 items. On the staff page, you want to sort people by menu order with no post limit. The recommended resources page should sort posts alphabetically without a post limit. You could set all those archive pages up by building a custom page template that uses a new WP_query with custom vars for each one, and assigning a Page to each template.

A cleaner solution is to use WordPress’s own template hierarchy to generate archives for each post type. For your custom post types (slugs: portfolio, staff, resource), you’d create archive-portfolio.php, archive-staff.php, and archive-resource.php. Those archive template files will be used whenever WordPress’s permalink URLs are used to call archives for each post type. By default, they’ll use WordPress’s default query vars: limit to 10 posts (or whatever number is saved in Settings > Reading) in descending order by date. We can add (and adjust) the following snippet in functions.php to modify the query vars used on each of those template pages:

add_action( 'pre_get_posts', 'custom_query_vars' );
function custom_query_vars( $query ) {
  if ( !is_admin() && $query->is_main_query() {
    if ( get_post_type() == 'portfolio' ) {
      $query->set( 'posts_per_page' => 12 );
    }
    if ( get_post_type() == 'staff' ) {
      $query->set( 'posts_per_page' => -1 );
      $query->set( 'orderby' => 'menu_order' );
      $query->set( 'order' => 'ASC' );
    }
    if ( get_post_type() == 'resource' ) {
      $query->set( 'posts_per_page' => -1 );
      $query->set( 'orderby' => 'title' );
      $query->set( 'order' => 'ASC' );
    }
  }
  return $query;
}

The first line of code in that block adds the function custom_query_vars() to the pre_get_posts WordPress action: any time WordPress runs a post query, our custom function will run with the ability to modify query vars.

In our custom function, the first thing we do is use an if statement to limit where our modifications happen. The !is_admin() condition prevents custom query modifications from affecting the Dashboard. The $query->is_main_query() condition makes sure our changes only happen to the main query on a given archive page (for example, sidebar widgets won’t be affected by our tweaks).

Inside that condition, we’ve got the three if statements we’ll need to modify each of our custom post type archives. Inside of each if, we use $query->set(); to change the appropriate query vars. For portfolio items, we change the posts_per_page var to 12. For the staff archive, we remove the post limit ('posts_per_page' => -1) and order items by menu_order in ascending order. For resource archive pages, we remove the post limit and order posts by their title in ascending order (alphabetical).

Note: $query->set( $var, $value ); is simply a WordPress alias function for query_vars[$var] = $value;. The function set_query_var( $var, $value ); does the same thing, but can run outside of the pre_get_posts action.

This code snippet can also change query vars on individual categories. For example, if you wanted the posts in a specific blog category to be ordered differently, you’d replace if ( get_post_type() == $post_type ) with if ( is_category( $category_slug ) ). For a custom taxonomy, you could use if ( is_tax( $taxonomy, $term ) ). WordPress has several conditional tags you can use to modify specific queries.