Order of search results based off of a backend custom field and also in alpha order

Question

I'm using WordPress as a searchable database of people, and I want to be able to sort search results by the person's last name. Initially, I figured I could sort the search results in just alpha, but it results in sorting them in alpha by their first name.

So I figured if I create a backend-only custom field for the person's last name, I could adjust the search result to display based on the custom field but in alpha order. I would want all search results to follow these rules.

Does this make sense, or is there an easier method I could try? I know I could do this with a plugin, but I would rather avoid using a plugin for such an integral part of what we need this to be. Plus, I want to know how it works so I can fix it if something breaks. haha.

This is the code I have been working from-it gets me the alpha part, but I don't know how to apply the custom field.

function abc_search( $query ) {
    if( $query->is_search ) {
        $query->set( 'orderby', 'title' );
        $query->set( 'order', 'ASC' );
    }
}
add_filter( 'pre_get_posts','abc_search' );

Answer 1

Surname is already stored as user meta last_name so you don't need a custom field. You do need to make sure you're only affecting the page you want to.

    function sort_users_by_lastname( $query ) {
        // only if we're on users.php
        // and when orderby isn't changed. the default (when nothing is set) is "login"
        $screen = get_current_screen();
        if ( $screen->base == 'users' && is_admin() && $query->get('orderby') === 'login') {

            // Set the orderby parameter to user's last name
            $query->set( 'meta_key', 'last_name' );
            $query->set( 'orderby', 'meta_value' );
            $query->set( 'order', 'ASC' );
        }
    }
    add_action( 'pre_get_users', 'sort_users_by_lastname' );