pre_get_posts

function target_main_category_query_with_conditional_tags( $query ) {
	if ( ! is_admin() && $query->is_main_query() ) {
		// Not a query for an admin page.
		// It's the main query for a front end page of your site.

		if ( is_category() ) {
			// It's the main query for a category archive.

			// Let's change the query for category archives.
			$query->set( 'posts_per_page', 15 );
		}
	}
}
add_action( 'pre_get_posts', 'target_main_category_query_with_conditional_tags' );

/**
*
*		The Code below will modify the main GeChiUI loop, before the queries fired,
*	to only show posts in the halloween category on the home page.
*
*/
	function sbt_exclude_category($query){
		
		if ( $query->is_home() && $query->is_main_query() && ! is_admin() ) {
			
			$query->set( 'category_name', 'halloween' );
		}
	}
	add_action('pre_get_posts','sbt_exclude_category');

function university_adjust_queries($query){
   if ( ! is_admin() && is_post_type_archive( 'event' ) && $query->is_main_query() ) {
        $query->set( 'meta_key', 'event_date' );
        $query->set( 'orderby', 'meta_value_num' );
        $query->set( 'order', 'ASC');
        $query->set( 'meta_query', array(
            array(
                'key'     => 'event_date',
                'compare' => '>=',
                'value'   => date('Ymd'),
                'type'    => 'numeric',
            )
        ) );
   }
}
add_action( 'pre_get_posts', 'university_adjust_queries' );