title: add_field logstash after converting value to Json
body: <p>I have logfile containing log in this form</p>
  
  <pre><code>"{\"user_id\":\"79\",\"timestamp\":\"2016-12-28T11:10:26Z\"‌​,\"operation\":\"ver‌​3 - Requested for recommended,verified handle information\",\"data\":\"\",\"content_id\":\"\",\"channel_id‌​\":\"\"}"
  </code></pre>
  
  <p>for which I have written logstash configuration</p>
  
  <pre><code>input {
  beats {
      port =&gt; "5043"
  }
  }
  filter{
      grok {
         match =&gt; { "message" =&gt; "%{QS:mydata}"}
      }
      json {
         source =&gt; "message"
         target =&gt; "parsedJson"
      }
      mutate {
         add_field =&gt;{
          "user_id" =&gt; "%{[parsedJson.user_id]}"
          "operation" =&gt; "%{[parsedJson][operation]}"
          "data"=&gt; "%{[parsedJson][operation]}"
         }
       }
  }
  output {
      elasticsearch {
         hosts =&gt; [ "localhost:9200" ]
      }
  }
  </code></pre>
  
  <p>basically I have tried many permutations to fetch the value but in elasticsearch data is like the image below. I am not able to fetch data from JSON and assign to a new value.
  please help.
  <a href="https://i.stack.imgur.com/Ij6Yx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ij6Yx.png" alt="enter image description here"></a></p>