title: Upgrading MongoDB C++ Driver to mongocxx-3.1.2
body: <p>How to upgrade from mongoDB C++ driver from Legacy to mongocxx-3.1.2 easly?
  What are the classes in mongocxx-3.1.2 for following?</p>
  
  <pre><code>mongo::BSONElement;
  mongo::BSONObj;
  mongo::BSONObjBuilder;
  </code></pre>
  
  <p>Thanks In Advance..</p>