Using pre_get_posts

gistfile1.txt

<?php 
	
	// example, set posts_per_page on CTP "book"
	function books_pre_get_posts($query=false) {
		if (is_admin() || 
				!$query || 
				!is_a($query, 'WP_Query') || 
				!$query->is_main_query()) {
			return;
		}
		if (isset($query->query_vars['post_type']) && 
				$query->query_vars['post_type'] == 'books') {
			$query->set('posts_per_page', 2);
			$query->set('order', 'DESC');
		}
	}
	add_action('pre_get_posts', 'books_pre_get_posts');
	
?>