title: dangerous to select fields in MongoDB Doctrine?
body: <p>I'm not sure whether this is my fault. But I find that select fields in mongodb doctrine queries can lead to horrible consequence.</p>
  
  <p>For example, I have a Page document like:</p>
  
  <pre><code>class Page
  {
      /**
       * @MongoDB\String
       */
      private $title;
  
      /**
       * @MongoDB\Int
       */
      private $nbClicks = 0;
  
      /**
       * @MongoDB\Int
       */
      private $nbShares = 0;
  
      // other fields ...
  }
  </code></pre>
  
  <p>I may write some query like</p>
  
  <pre><code>$queryBuilder-&gt;select('title')-&gt;getQuery()-&gt;execute();
  </code></pre>
  
  <p>And somewhere behind this I do</p>
  
  <pre><code>$dm-&gt;flush();
  </code></pre>
  
  <p>nbClicks and nbShares of Pages I retrieved earlier are set to 0.</p>
  
  <p>Is this something expected or might be a bug?</p>
  
  <p>Thank you!</p>