MongoDB Aggregation with the sum of array values

Question

I have a collection with the 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 I would like to perform aggregation so that I know for a specific passenger, since it was with a specific driver, in my example it would be: for user1: [{ driver: user2, times: 2}] for user2: [{ driver: user1, times: 2}] for user3:[{ driver: user1, times: 3}, {driver: user2, times:2}]

Im brand new with mongo and knows how to perform easy aggregation with the sum, but not when its internal arrays, and when my object itself is in the array. what is the appropriate way to do this kind of aggregation and, more specifically, how do I execute it on an express.js based server?

Answer 1

, $match , , $unwind, . $match , , , $project. , user3 :

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

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

UPDATE

, , $group $project, $sum:

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
        }
     }
])

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