$query->set( 'post_type', 'post' ); not working

Question

I am trying to exclude pages from my search result with this function:

function posts_for_current_author($query) {
    global $user_level;

    if($query->is_admin && $user_level < 5) {
        global $user_ID;
        $query->set('author',  $user_ID);
        unset($user_ID);
    }
    unset($user_level);


    if ($query->is_search && $query->is_main_query()) {
        $query->set('posts_per_page', 9);
        $query->set( 'post_type', 'post' );
    }
    return $query;
}
add_filter('pre_get_posts', 'posts_for_current_author');

In if($query->is_search) i have a $query->set( 'post_type', 'post' ); but that one does not want to work, even though $query->set('posts_per_page', 9); works... So my mind is blown here. Anyone know how to fix this?

Answer 1

After Milo's help I found a function where it altered the search query:

if( is_search() && empty($_GET['post_type']) && !is_admin() ) {
                global $wpdb;
                $query = get_search_query();
                $query = $wpdb->esc_like( $query );

                $where .= " OR {$wpdb->posts}.ID IN (";
                $where .= "SELECT {$wpdb->postmeta}.post_id ";
                $where .= "FROM {$wpdb->posts}, {$wpdb->postmeta} ";
                $where .= "WHERE {$wpdb->posts}.post_type = 'page' ";<-page to post
                $where .= "AND {$wpdb->posts}.post_status = 'publish' ";
                $where .= "AND {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id ";
                $where .= "AND {$wpdb->postmeta}.meta_key IN('above-sidebar', 'content-with-sidebar', 'below-sidebar') ";
                $where .= "AND {$wpdb->postmeta}.meta_value LIKE '%$query%' )";
            }
            return $where;

I changed post_type ='page' to 'post' and now it works perfectly.

Thanks again, Milo!

Cheers