Mongodb aggregate: convert date to another timezone -

i save transaction :

{code: "a", total: 250000, timestamp: isodate("2016-01-20t23:57:05.771z")}, {code: "b", total: 300000, timestamp: isodate("2016-01-20t05:57:05.771z")} 

each of transaction has timestamp field under utc timezone in it. since live in jakarta (utc+7) timezone, need add 7 hours timestamp before aggregation. here's mongo syntax:

db.transaction.aggregate( [  {    $project:      {        year: { $year: "$timestamp" },        month: { $month: "$timestamp" },        day: { $dayofmonth: "$timestamp" }      }  } ]) 

it returns:

    {         "_id" : objectid("56a01ed143f2fd071793d63b"),         "year" : 2016,         "month" : 1,         "day" : 20     },     {         "_id" : objectid("56a01ed143f2fd071793d63b"),         "year" : 2016,         "month" : 1,         "day" : 20     } 

which wrong since first transaction (code a), happened @ 21st january, since converted utc (-7 hours), became isodate("2016-01-20t23:57:05.771z")

note: i'm aware about same problem on here, here's i've been tried far:

db.transaction.aggregate( [  {$project: {"timestamp": {$add: [7 * 60 * 60 * 1000]}}},  {    $project:      {        year: { $year: "$timestamp" },        month: { $month: "$timestamp" },        day: { $dayofmonth: "$timestamp" }      }  } ]) 

but returns can't convert bson type numberdouble date error. suggestions?

you need add "timestamp" 7 * 60 * 60 * 1000 can in 1 $project stage.

db.collection.aggregate([     { "$project": {         "year": { "$year": { "$add": [ "$timestamp", 7 * 60 * 60 * 1000 ] } },          "month": { "$month": { "$add": [ "$timestamp", 7 * 60 * 60 * 1000 ] } },          "day": { "$dayofmonth": { "$add": [ "$timestamp", 7 * 60 * 60 * 1000 ] } }      } } ]) 

which returns:

{         "_id" : objectid("56a07f8f8448ed9fd2359365"),         "year" : 2016,         "month" : 1,         "day" : 21 } {         "_id" : objectid("56a07f8f8448ed9fd2359366"),         "year" : 2016,         "month" : 1,         "day" : 20 }