gistfile1.js

db.events.find({"name":"purchased_deal","is_first_time":{$exists:false}}).forEach(function(data) {
   var query = {
     "name" : data.name,
     "user_id" : data.user_id,
     "date_created": { $lt : data.date_created }
   }

  if(db.events.count(query) == 0) {
    data.is_first_time = true
  } else {
    data.is_first_time = false
  }

  db.events.save(data)

});