MongoDB Aggregation with sum of array values -

i have collection following data:

{     "_id" : objectid("5516d416d0c2323619ddbca8"),     "date" : "28/02/2015",     "driver" : "user1",     "passengers" : [         {             "user" : "user2",             "times" : 2         },         {             "user" : "user3",             "times" : 3         }     ] } {     "_id" : objectid("5516d517d0c2323619ddbca9"),     "date" : "27/02/2015",     "driver" : "user2",     "passengers" : [         {             "user" : "user1",             "times" : 2         },         {             "user" : "user3",             "times" : 2         }     ] } 

and perform aggregation know passenger, times driver, in example be: user1: [{ driver: user2, times: 2}] user2: [{ driver: user1, times: 2}] user3: [{ driver: user1, times: 3}, {driver: user2, times:2}]

im quite new mongo , know how perform easy aggregation sum, not when inside arrays, , when subject in array. appropriate way perform kind of aggregation, , in more specific, how perform in express.js based server?

to achieve needs aggregation framework, first pipeline stage $match operation on passenger in question matches documents user in passenger array, followed $unwind operation deconstructs passengers array input documents in previous operation output document each element. $match operation on deconstructed array follows further filters previous document stream allow matching documents pass unmodified next pipeline stage, projecting required fields $project operator. aggregation pipeline user3 like:

db.collection.aggregate([      {         "$match": {             "passengers.user": "user3"         }      },      {          "$unwind": "$passengers"      },      {         "$match": {             "passengers.user": "user3"         }      },      {          "$project": {              "_id": 0,             "driver": "$driver",             "times": "$passengers.times"         }      } ]) 

result:

/* 0 */ {     "result" : [          {             "driver" : "user1",             "times" : 3         },          {             "driver" : "user2",             "times" : 2         }     ],     "ok" : 1 } 

update:

for grouping duplicates on drivers different dates, mentioned can $group operation before last $project pipeline stage compute total passengers times using $sum operator:

db.collection.aggregate([      {         "$match": {             "passengers.user": "user3"         }      },      {          "$unwind": "$passengers"      },      {         "$match": {             "passengers.user": "user3"         }      },      {          "$group": {              "_id": "$driver",               "total": {                  "$sum": "$passengers.times"              }          }      },      {          "$project": {             "_id": 0,             "driver": "$_id",             "total": 1         }      } ]) 

result:

/* 0 */ {     "result" : [          {             "total" : 2,             "driver" : "user2"         },          {             "total" : 3,             "driver" : "user1"         }     ],     "ok" : 1 }