title: Yii2: Use NOT EXISTS or NOT IN
body: <p>How do I use the conditions "not exist" and "not in" in Yii2?
  I have a select with the list of users, but want to exclude users who are on the table "user_post"</p>
  
  <p>User</p>
  
  <blockquote>
    <p>id_user | username</p>
  </blockquote>
  
  <p>User_post</p>
  
  <blockquote>
    <p>id_user_post | id_post | id_user</p>
  </blockquote>
  
  <pre><code> &lt;?= $form-&gt;field($model, 'id_user')-&gt;dropDownList(
           ArrayHelper::map(User::find()
  
                  -&gt;all(),'id_user','username'),
          ['prompt' =&gt; 'Select User']
      ) ?&gt;
  </code></pre>