mongoose/mongoDB/nodeJS populate query result

result.json

{
  "_id": "56f13b504666f77e4652bbf3",
  "user_id": "la6m5a1ha",
  "uname": "lol",
  "__v": 0,
  "notify_options_fk_key": {
    "_id": "56f13ba94666f77e4652bbf4",
    "__v": 1,
    "bid_opt_container": [
      {
        "_id": 1,
        "bid_opt": "set_bid"
      },
      {
        "_id": 3,
        "bid_opt": "del_bid"
      }
    ],
    "ask_opt_container": [],
    "buy_opt_container": [
      {
        "_id": 1,
        "trade_opt": "buy_keyword_on_highest_bid"
      },
      {
        "_id": 2,
        "trade_opt": "buy_keyword_on_set_ask"
      }
    ],
    "updated_on": "2016-03-22T12:36:47.527Z"
  },
  "createdOn": "2016-03-22T12:32:16.945Z"
}