Query all post types but limit to parents

Question

I'm building a site with several post types and am using a single index.php to query the archive for each one in turn. One of these post types is hierarchical and I'd like to just query the parent. I can use query_posts to limit to 'post_parent' => 0 but that creates a new query and resets the post type argument meaning that I'd have to create separate queries for each post type.

Is there a way to limit while ( have_posts() ) : the_post(); to parents only without creating a new query?

Answer 1

In your functions.php you can create a function that will hook into the pre_get_posts hook. Something like (just an example):

function alter_query($query){
  $query->set('post_parent', 0);
}
add_action( 'pre_get_posts', 'alter_query' );

There you can alter the main query. That way while(have_posts()) : the_post(); will still just normally work. (You should check if you are altering the right query and such. Otherwise the post_parent will be applied to all query's by wordpress. You don't want that).

The BIG advantage is, that if you alter the main query, you only have to do that. Wordpress will still select the appriopiate template and such. If you also want to alter the template loaded, you can use the template_redirect hook.