mongodb - How to fill missing field with data to existing documents in mongo db? -

i have documents like

   [{ _id:.., mailtitle:"hello", broadcastmessage:"how u"}]    [{ _id:.., mailtitle:"hello john", broadcastmessage:"how u john"}]    [{ _id:.., mailtitle:"hello", broadcastmessage:"how u john",    user_id:"1", datesent:"12/12/2016"    }] 

now want add user_id:"1", datesent:"12/12/2016" first 2 , others documents.

please help!!!

using update (deprecated) :

 db.collection.update(            { "user_id": {$exists: false}, "datesent": {$exists: false} },            { $set:               {                 user_id : 1,                 datesent: "12/12/2016", (use utc date object instead of string)               }            },         {             multi: true         }     ); 

using updatemany :

db.collection.updatemany(       { "user_id": {$exists: false}, "datesent": {$exists: false} },       { $set:               {                 user_id : 1,                 datesent: "12/12/2016", (use utc date object instead of string)               }       }    ); 

the above pick documents don't have field called user_id , datesent, , set fields. hope helps.