title: In Mongoose+NodeJS is pushing an object into array the same as pushing the objectID
body: <p>In Mongoose Schema's which involve Users, we sometimes see something like this: </p>
  
  <pre><code>var UserSchema = new mongoose.Schema({
    followers: [{type: mongoose.Schema.Types.ObjectId, ref: 'User'}] 
  });
  </code></pre>
  
  <p>If somewhere in my code, I want to add a follower, are the following two statements equivalent?</p>
  
  <p><strong>First possibility</strong></p>
  
  <pre><code>var aUser = new User();
  var anOtherUser = new User();
  aUser.followers.push(anOtherUser); //Push the user object
  </code></pre>
  
  <p><strong>Second Possibility</strong></p>
  
  <pre><code>var aUser = new User();
  var anOtherUser = new User();
  aUser.followers.push(anOtherUser._id); //Push the id directly
  </code></pre>