gistfile1.txt

Table
public function validationDefault(Validator $validator)
{
        $validator
            ->requirePresence('device_id', 'create')
            ->notEmpty('device_id');
            
        return $validator;
}

Controller

public function custom()
{
        $tag = $this->Tags->newEntity();
        if ($this->request->is('post')) {
          $tag = $this->Tags->patchEntity($tag, $this->request->data);
          if (!$tag->errors()) {
                $post = $this->Tags->Posts->get($tag->post_id);
                $tag->number = $post->number;
                $this->Tags->save($tag);
          }
        }
}