title: Eloquent how to do something when delete or update operate on a special model
body: <p>Most of my db table contain <code>create_user_id</code> and <code>update_user_id</code></p>
  
  <p>How can l update this two field automatic when l use <code>save()</code>, <code>update()</code>, <code>insert()</code>, <code>createOrUpdate()</code> and etc method.</p>
  
  <p>For example, l execute this script:</p>
  
  <pre><code>$model = Model::find(1);
  $model-&gt;model_f = 'update';
  $model-&gt;save();
  </code></pre>
  
  <p>then this record's <code>model_f</code> updated, and <code>update_user_id</code> updated, too.</p>
  
  <p>l know eloquent can manage <code>update_time</code> automatic and l have use it already. But l want to do something else when update or insert or delete</p>
  
  <p>PS: l have a constant named <code>USERID</code> to remember current user's id</p>