title: Yii2 error - Class 'yii\mongodb\ActiveRecord' not found
body: <p>I have done setup for mongodb on my system with Yii2 basic.</p>
  
  <p>I have also installed the extension for mongodb (yii2-mongodb) inside a directory /vendor/yiisoft and checked for the permissions.</p>
  
  <p>Now I am testing the connection with a controller and model but I am getting the following error.</p>
  
  <blockquote>
    <p>PHP Fatal Error – yii\base\ErrorException Class</p>
    
    <p>'yii\mongodb\ActiveRecord' not found</p>
  </blockquote>
  
  <p>Is there anything that needs to be installed?</p>