title: MongoDB: Converting String to Date within Projection
body: <p>I got the following MongoDQ query:</p>
  
  <pre><code>db.entries.aggregate([
    {"$sort" : {"display_time" : -1}}, 
    {"$project": { 
              "ts":  { "$max": "$display_time" } ,
              "value": { "$avg": "$price" }
      }
  }
  ]);
  </code></pre>
  
  <p>, where display_time is a String of the format "2018-07-20T15:45:00+02:00".
  I am trying to convert it to a timestamp, but couldn't get it done.</p>
  
  <p>Is there anyone that could help, please?</p>
  
  <p>Thank you! :)</p>