title: Get data from different collections (.files , .chunks and master data) in MongoDB
body: <p>I am trying to upload the user details along with picture in the mongoDB using GridFS and multer. I need to get the data along with all the pictures to be displayed in the tabular form in client side(using angular).</p>
  <p>The problem is the picture is getting stored in user.files and user.chunk collections, where as the other data like userID, userDesignation, userName is stored in user collection. How could I retrieve the data from both the collections in one GET userData API?</p>
  <p>there is a option for merge the data using <code>$lookup</code> but that needs to have a common key in both the collections, whereas in my case there is common key.</p>