title: How can I set an attribute in every subdocument in MongoDB?
body: <p>If I have a document like:</p>
  
  <pre><code>{title: "hello", 
   formats:{mp4: {status: "processing"},
            webm: {status: "processing" }} }
  </code></pre>
  
  <p>How can I write a $set query to set both inner status to "completed"</p>