如果满足条件，如何在数据库中初始化表对象？ cakephp

Question

我想为类表创建一个等待列表。因此，如果已报名上课的学生人数已满，则所有新注册的学生都将被放入候补表。管理员可以指定一个班级是否有候补名单。如果管理员批准了该学生，则可以将其注册为该班级。类控制器中的add函数是

public function add()
{
    $class = $this->Classes->newEntity();
    if ($this->request->is('post')) {
        $class = $this->Classes->patchEntity($class, $this->request->getData());
        if ($this->Classes->save($class)) {
            $this->Flash->success(__('The class has been saved.'));

        $this->loadModel('Lessons');

        $date = $class->start_date;

        // Create lessons for eack week of the class
        while($date <= $class->end_date) {

            // Get the next lesson date after the start of the user's enrolment, then each week afterward using the loop

            $lesson = $this->Lessons->newEntity();
            $lesson->class_id = $class->id;
            $lesson->teacher_id = $class->teacher_id;
            $lesson->lesson_date = $date;

            $this->Lessons->save($lesson);

            $date = $date->modify('+1 week');
        }

        $choice = $class->waitlist;
        if ($choice == "yes"){
            $this ->loadModel('Waitlist');
        }

        return $this->redirect(['controller' => 'schools', 'action' => 'view', $class->school_id]);
    }
    $this->Flash->error(__('The class could not be saved. Please, try again.'));
}
$schools = $this->Classes->Schools->find('list', ['limit' => 200]);
    $this->loadModel('Teachers');
    $teachers = $this->Teachers->find('list');



$this->set(compact('class', 'schools', 'teachers'));
$this->set('_serialize', ['class']);
}

waitlist表具有以下字段：waitlist_id，class_id，student_id和index。
类表中的字段waitlist_id是外键。