onBeforeSaveUser validation for existing user but not new user

Question

I am trying to validate first name and last name on my user registration form. I have tested and the following works for existing users when updating their profile via the form. Both use the onBeforeSaveUser event.

Any ideas why this wouldn't validate for registering users?

public function init()
{
    craft()->on('users.onBeforeSaveUser', function(Event $event)
    {
        craft()->businessLogic_events->onBeforeSaveUser($event);
    });
}

public function onBeforeSaveUser(Event $event)
{
    $user = $event->params['user'];

    if (empty($user->firstName))
    {
        $user->addError('firstName', Craft::t('Name cannot be empty.'));
        $event->performAction = false;
    }

    if (empty($user->lastName))
    {
        $user->addError('lastName', Craft::t('Last Name cannot be empty.'));
        $event->performAction = false;
    }
}

Answer 1

If you hit the submit button and don't fill out any fields. Then the only errors back are Email and Password (standard and set out by Craft). If you do enter an email and password then my validation code works and it errors again this time with the firstName and lastName errors. But these don't trigger on first submit when all fields are blank.

This is a known issue (specifically with the UserModel when saving a user) because "First Name" and "Last Name" aren't true fields in Craft, but more special case fields.

When saving a user, the UserModel validation runs first and immediately bails when the validation error occurs before the onBeforeSaveUser event fires not giving any plugins a chance to participate.

This will be fixed in the upcoming Craft 3 release.