title: How to add new filed by type data to existing documents Mongodb?
body: <p>I am trying to add field(key) existing document all records. And i wanna; when new record saved, automaticly save to current date this field;</p>
  
  <p>Now my one document instance of studen
  {
    "_id" : ObjectId("4f83ed9bcba9560ea474465d"),
    "name" : "",
    "lastname" : "",
    "number" : "",
     .....
  }</p>
  
  <p>I want to this;</p>
  
  <p>{
    "_id" : ObjectId("4f83ed9bcba9560ea474465d"),
    "name" : "",
    "lastname" : ""
    "Date" :  currentTime()
  }</p>
  
  <p>When new record saved to document automaticly save current time to documents. 
  I dont wanna do this from client side,</p>