title: Join like query in mongodb
body: <p>i have a requirement where i need to get the friends of user. I have made two collections named User and Friends. 
  The code that i use to access the data from the Friends and User is:</p>
  
  <pre><code>var friend = Friends.find({acceptor:req.currentUser.id,status:'0'},function(err, friends) {
      console.log('----------------friends-----------------'+friends.length);
  
    });
  </code></pre>
  
  <p>console.log is giving me the desired results for friends.Now if i use friend to access the User data like the one given i am not getting the result that i need.</p>
  
  <pre><code>var user = User.find({_id:friend.requestor},function(err, users) { 
       console.log('----------------user-----------------'+users.length);
  });
  </code></pre>
  
  <p>how can i join the two queries to get the desired result.Please help</p>