CakePHP 中如何防止重复提交表单？

echo $this->Form->create($post);
echo $this->Form->control('title');
echo $this->Form->control('body');
echo $this->Form->end(__('Submit'));

echo $this->Form->create($post, ['type' => 'post']);
echo $this->Form->control('title');
echo $this->Form->control('body');
echo $this->Form->token('token');
echo $this->Form->end(__('Submit'));

document.getElementById("submit-btn").addEventListener("click", function() {
  document.getElementById("submit-btn").disabled = true;
});

public function add() {
  $post = $this->Posts->newEmptyEntity();
  if ($this->request->is('post')) {
    $data = $this->request->getData();
    if (!$this->Posts->exists(['title' => $data['title'], 'body' => $data['body']])) {
      $post = $this->Posts->patchEntity($post, $data);
      if ($this->Posts->save($post)) {
        $this->Flash->success(__('The post has been saved.'));
        return $this->redirect(['action' => 'index']);
      }
      $this->Flash->error(__('The post could not be saved. Please, try again.'));
    } else {
      $this->Flash->error(__('The post already exists.'));
    }
  }
  $this->set(compact('post'));
}