title: Mongoose ODM findOneAndUpdate sub-document
body: <p>I currently have a <strong>Message</strong> schema which has a sub-document of replies as such:</p>
  
  <pre><code>message: String,
  replies: [{
     message: String,
     userFrom: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User'
     }
   }]
  </code></pre>
  
  <p>I am attempting to make a POST request that will allow me to findOneAndUpdate the message to attach a reply. I've attempted the following:</p>
  
  <pre><code>Message.findOneAndUpdate(req.params.id,{
    replies: {
      message: req.body.reply,
      userFrom: req.user._id
    }
  }, function(err, data){
    ...
  });
  </code></pre>
  
  <p>What is happening is I am overwriting any reply that is currently in the replies array. I believe I need to use the $push operator but I'm not quite sure how.</p>
  
  <p>Is it possible to use findOneAndUpdate as well as $push in a single request?</p>