title: What is the difference between Model.findOne() & Model.findById() in Mongoose?
body: <p>Consider we are searching a document from MongoDB based on the _id value. Which one of the following code is efficient ?</p>
  
  <ol>
  <li><p><code>ModelObj.findById(IdValue).exec(callback);</code></p></li>
  <li><p><code>ModelObj.findOne({ '_id': IdValue}).exec(callback);</code></p></li>
  </ol>
  
  <p>I feel ModelObj.findById() is efficient, but what are the supportive reasons or How is it efficient?</p>