title: Mongoose/Mongodb: Exclude fields from populated query data
body: <p>I use the following mongoose query in a MEAN-environment to find and output a particular author and his corresponding books. </p>
  
  <pre><code>Author
  .findOne({personcode: code})
  .select('-_id')
  .select('-__v')
  .populate('bookids') //referencing to book documents in another collection (-&gt;array of bookids)
  .select('-_id') //this doens't affect the data coming from the bookids-documents
  .select('-__v') //this doens't affect the data coming from the bookids-documents
  .exec(function (err, data) {
     //foo
  });
  </code></pre>
  
  <p>I would also like to exclude the "_id" and "__v" fields from the populated data coming from the external documents. How can that be achieved?</p>