WPMU Membership 2: Adding more column in billing table and sorting example

code.php

<?php
/**
 * Example: Member first name and last name and sorting ASC and DESC
 */
 
add_filter( 'ms_helper_listtable_billing_get_columns', function( $columns, $currency ) {
    
    $columns['first_name'] = 'First Name';
    $columns['last_name'] = 'Last Name';
    
    return $columns;
}, 10, 2 );

add_filter( 'ms_helper_listtable_billing_default_column', function( $html, $item, $column_name, $this ) {
    $member = MS_Factory::load( 'MS_Model_Member', $item->user_id );
    switch( $column_name )
    {
        case 'first_name':
            return $member->first_name;
            break;
        
        case 'last_name':
            return $member->last_name;
            break;
        
        default:
            return $html;
    }
}, 10, 4 );

add_filter( 'ms_helper_listtable_billing_sortable_columns', function( $columns ) {
    $columns['first_name'] = array( 'first_name', false );
    $columns['last_name'] = array( 'last_name', false );
    
    return $columns;
}, 10, 1);

add_filter( 'ms_model_invoice_get_invoices', function( $invoices, $args ) {
    
    if( $args['orderby'] == 'first_name' || $args['orderby'] == 'last_name' )
    {
        foreach( $invoices as $key => $invoice )
        {
            $user_id = $invoice->user_id;
            $member = MS_Factory::load( 'MS_Model_Member', $user_id );
            
            $invoices[$key]->_saved_data['first_name'] = $member->first_name;
            $invoices[$key]->_saved_data['last_name'] = $member->last_name;
        }
        
        usort($invoices, "cmp_" . $args['orderby'] . '_' . $args['order']);
    }
    
    return $invoices;
}, 10, 2 );

function cmp_first_name_asc($a, $b)
{
    return strcmp($a->_saved_data['first_name'], $b->_saved_data['first_name']);
}

function cmp_first_name_desc($a, $b)
{
    return strcmp($b->_saved_data['first_name'], $a->_saved_data['first_name']);
}

function cmp_last_name_asc($a, $b)
{
    return strcmp($a->_saved_data['last_name'], $b->_saved_data['last_name']);
}

function cmp_last_name_desc($a, $b)
{
    return strcmp($b->_saved_data['last_name'], $a->_saved_data['last_name']);
}