{
    "_id": 681
    "sensors": [
            {
                "type": "foo"
            },
            {
                "type": "bar"
            }
    ]
}

{
    "_id" : ObjectId("570cc8b6ac55850d5740784e"),
    "timestamp" : ISODate("2016-04-12T12:06:46.344Z"),
    "type" : "foo",
    "nodeid" : 681,
    "value" : 10
}

{
    "_id" : ObjectId("190ac8b6ac55850d5740776e"),
    "timestamp" : ISODate("2016-04-12T12:06:46.344Z"),
    "type" : "bar",
    "nodeid" : 681,
    "value" : 20
}

{
    "_id" : ObjectId("167bc997bb66750d5740665e"),
    "timestamp" : ISODate("2016-04-12T12:06:46.344Z"),
    "type" : "bar",
    "nodeid" : 200,
    "value" : 20
}

{
    "_id" : ObjectId("110cc9c6ac55850d5740784e"),
    "timestamp" : ISODate("2016-04-09T12:06:46.344Z"),
    "type" : "foo",
    "nodeid" : 681,
    "value" : 12
}

{
    "_id": 681
    "sensors": [
            {
                "_id" : ObjectId("570cc8b6ac55850d5740784e"),
                "timestamp" : ISODate("2016-04-12T12:06:46.344Z"),
                "type" : "foo",
                "nodeid" : 681,
                "value" : 10
            },
            {
                "_id" : ObjectId("190ac8b6ac55850d5740776e"),
                "timestamp" : ISODate("2016-04-12T12:06:46.344Z"),
                "type" : "bar",
                "nodeid" : 930,
                "value" : 20
            }
    ]
}

db.nodes.aggregate(
        [
            {
                $unwind: "$sensors"
            },
            {
                $match:{
                    nodeid: 681
                       }
            },
            {
                $lookup:{
                        from: "values", localField: "sensors.type", foreignField: "type", as: "sensors"
                    }
             }
         }
    ]
)