Answered [xPDO] How to update 2 related objects while adding a new one the relationship?

$process->set('request',(int) $request->get('id'));
$process->set('customer', (int) $request->get('customer'));

if (isset($_POST['submit'])) {
    // Form has been submitted 
    $process = $modx->newObject('quoteProcess');
    //$process->fromArray($process_fields);
    $process->set('request',(int) $request->get('id'));
    $process->set('customer', (int) $request->get('customer'));
    if ($process->save()) {
...
}

$output = '<p>ID: ' . $request->get('id') . '</p>';
$output .= '<p>CUSTOMER: ' . $request->get('customer') . '</p>';
die($output);