title: NodeJS and MongoDB - Array of ObjectId how to return Objects
body: <p>I have in a collection an reference array of ObjectId. And I want to return the object's data linked with those Ids in the json response.</p>
  
  <pre><code>retrieveFromUser: function( req, res ) {
      var user_id =   req.params.user_id;
      User.findById( user_id, function( err, user ) {
          if( err ) {
              res.send( 404, "Unable to find user");
          } else {
              // This returns the array but I want the objects data
              return res.json( user.constructions );
          }
      });
  }
  </code></pre>
  
  <p>How can I do that ?<br/>
  thanks a lot !</p>