title: Find by _id on an array of objects in mongodb database
body: <p>I'm trying to find the id of an object inside an array of objects. That _id has the same field name _id as others in the document.
  This is my model (brief)</p>
  
  <pre><code>var CardSchema = new mongoose.Schema({
    beName: String,
    beLink: String,
    cards: [{ 
      cardType: String,
      cardBundle: String
    }]
  </code></pre>
  
  <p>This is an sample of my database content</p>
  
  <pre><code>_id: ObjectId(5a52540638086448bf4235e8)
  beName: Name1
  beLink: Link1
  cards: Array
   0: Object
      cardType: type1
      cardBundle: 1
      _id: ObjectId(5a526749d0ddab4bcdcc1556)
   1: Object
      cardType: type2
      cardBundle: 1
      _id: ObjectId(5a526749d0ddab4bcdcc1557)
  
  ...
  
  _id: ObjectId(5a52540638086448bf4235e9)
  beName: Namex
  beLink: Linkx
  cards: Array
   0: Object
      cardType: typex
      cardBundle: x
      _id: ObjectId(5a526749d0ddab4bcdcc1598)
   1: Object
      cardType: type2
      cardBundle: 1
      _id: ObjectId(5a526749d0ddab4bcdcc1599)
  </code></pre>
  
  <p>I'm trying to find the id of an specific card like this</p>
  
  <pre><code>Cards.find({ _id: req.params.id}, function (err, post) {
      if (err) return next(err);
      res.json(post);
    });
  </code></pre>
  
  <p>But I get an empty result</p>
  
  <p>I also tried</p>
  
  <pre><code>Cards.find({ _id: new ObjectId(req.params.id)}...
  </code></pre>