title: How to do a find iterating in a array field
body: <p>Hi i have a expressjs app using mongodb.</p>
  
  <p>At first i find a tv by id on my "tvs" collection, i get it but now i want to find all user info from other collection "users".</p>
  
  <p>This is my JSON for each collection:</p>
  
  <p><strong>tvs</strong></p>
  
  <pre><code>{
    "_id" : ObjectId("5203af83396d285ea2ecff8f"),
    "brand" : "LG",
    "comments" : [{
        "user" : ObjectId("521dc636eda03d0f9cab3568"),
        "text" : "Sold!"
      }, {
        "user" : ObjectId("521b2785eda03d0f9cab3566"),
        "text" : "Nice TV"
      }],
    "model" : "47LS5600",
    "price" : 499.0
  }
  </code></pre>
  
  <p><strong>users</strong></p>
  
  <pre><code>{
    "_id" : ObjectId("521b2785eda03d0f9cab3566"),
    "name" : {
      "first" : "Ruben",
      "last" : "Montes"
    }
  }
  </code></pre>
  
  <p>And this is my code</p>
  
  <pre><code>var tvs = db.collection("tvs");
  var users = db.collection("users");
  
  exports.findById = function (req, res) {
      var id = req.params.id;
      tvs.findOne({'_id': new BSON.ObjectID(id)}, function (err, tv) {
          users.find( { _id : tv.comments.user_id }).toArray(function (err, items) {
              res.send( { tv: tv, users: items } );
          }); 
  
      })
  }
  </code></pre>
  
  <p>I need to know how to iterate the comments array from tvs collection to get the the info user that post a comment</p>
  
  <pre><code>users.find( { _id : tv.comments.user_id })
  </code></pre>