title: mongodb update all document with incrementing the value by 1
body: <p>i have several document in mongoDB, doc structure is like this</p>
  
  <pre><code>{
  "a":"abc",
  "myid":2
  }
  </code></pre>
  
  <p>I want to update "myid" of all document with 1. for example for 1st document myid = 1, for second document myid =2 and so on. Is there a query?</p>