title: Why can't you modify the data returned by a Mongoose Query (ex: findById)
body: <p>When I try to change any part of the data returned by a Mongoose Query it has no effect.</p>
  
  <p>I was trying to figure this out for about 2 hours yesterday, with all kinds of <code>_.clone()</code>s, using temporary storage variables, etc. Finally, just when I though I was going crazy, I found a solution. So I figured somebody in the future (fyuuuture!) might have the save issue.</p>
  
  <pre><code>Survey.findById(req.params.id, function(err, data){
      var len = data.survey_questions.length;
      var counter = 0;
  
      _.each(data.survey_questions, function(sq){
          Question.findById(sq.question, function(err, q){
              sq.question = q; //has no effect
  
              if(++counter == len) {
                  res.send(data);
              }
          });
      });
  });
  </code></pre>