How to get aggregate Pipline result using MongoDB in golang mgo.v2 liabry
<p>Question background is I want retrieve aggregated data from MongoDB data by using golang mgo.v2 liabary.</p>

<p>I have a collection dataset as following.collection name is useragents</p>

<pre><code>{
    "_id" : ObjectId("57f940c4932a00aba387b0b0"),
    "tenantID" : 1,
    "date" : "2016-10-09 00:23:56",
    "venueList" : [
        {
            "id" : “VID1212”,
            "sum" : [
                {
                      "name" : "linux",
                      "value" : 12
                },
                {
                    "name" : "ubuntu",
                    "value" : 4
                }
            ],
            “ssidList” : [    // this is list of ssid’s in venue
                {
                    "id" : “SSID1212”,
                    "sum" : [
                        {
                            "name" : "linux",
                            "value" : 8
                        },
                        {
                            "name" : "ubuntu",
                            "value" : 6
                        }
                    ],
                    “macList” : [  // this is mac list inside particular ssid  ex: this is mac list inside the SSID1212
                        {
                            "id" : “12:12:12:12:12:12”,
                            "sum" : [
                                {
                                    "name" : "linux",
                                    "value" : 12
                                },
                                {
                                    "name" : "ubuntu",
                                    "value" : 1
                                }
                            ]
                        }
                    ]
                }
            ]
        },
        {
            "id" : “VID4343”,
            "sum" : [
                {
                     "name" : "linux",
                     "value" : 2
                }
            ],
            "ssidList" : [
                {
                    "id" : “SSID4343”,
                    "sum" : [
                        {
                            "name" : "linux",
                            "value" : 2
                        }
                    ],
                    "macList" : [
                        {
                            "id" : “43:43:43:43:43:34”,
                            "sum" : [
                                {
                                    "name" : "linux",
                                    "value" : 2
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}
</code></pre>

<p>I have already solved MongoDB shell script that i want by help from stack-overflow community.but I am troubling on when I was implemening it in golang using mgo.v2 library.</p>

<p>This is mongodb shell script</p>

<pre><code>db.useragents.aggregate([
    { "$match": { "venueList.id": { "$in": ["VID1212", "VID4343"] } } },
    { "$unwind": "$venueList" },
    { "$match": { "venueList.id": { "$in": ["VID1212", "VID4343"] } } },
    { "$unwind": "$venueList.sum" },    
    { 
        "$group": {
            "_id": "$venueList.sum.name",
            "count": { "$sum": "$venueList.sum.value" }
        }
    },
    { 
        "$group": {
            "_id": null,
            "counts": {
                "$push": {
                    "name": "$_id",
                    "value": "$count"
                }
            }
        }
    }
])
</code></pre>

<p>Please go though <a href="https://stackoverflow.com/questions/39943111/retrieve-item-list-by-checking-multiple-attribute-values-in-mongodb-in-golang">question background</a> </p>

<p>And I implement golang code as following</p>

<pre><code>func GetBrowserStats(constrains models.Constrains) ([]bson.M, error) {

    session := commons.GetMongoSession()
    defer session.Close()
    var col = session.DB("analytics").C("useragents")

    pipeline1 := bson.M{
        "$match": bson.M{
            "venueList.id": bson.M{
                "$in": []string{"VID1212", "VID4343"},
            },
        },
    }
    pipeline2 := bson.M{
        "$unwind": "$venueList",
    }
    pipeline3 := bson.M{
        "$match": bson.M{
            "venueList.id": bson.M{
                "$in": []string{"VID1212", "VID4343"},
            },
        },
    }
    pipeline4 := bson.M{
        "$unwind": "$venueList.sum",
    }

    pipeline5 := bson.M{
        "$group": bson.M{
            "_id": "$venueList.sum.name",
            "count": bson.M{
                "$sum": "$venueList.sum.value",
            },
        },
    }
    pipeline6 := bson.M{
        "$group": bson.M{
            "_id": bson.NewObjectId(),
            "counts": bson.M{
                "$push": bson.M{
                    "name":  "$_id",
                    "value": "$count",
                },
            },
        },
    }

    all := []bson.M{pipeline1, pipeline2, pipeline3, pipeline4, pipeline5, pipeline6}
    pipe := col.Pipe(all)

    result := []bson.M{}
    err := pipe.All(&amp;result)
    println(result[0])
    if err != nil {
        println(err.Error())
        errMsg := "Error occourred while getting dashboard configs from mongo stack:" + err.Error()
        log.Error()
        return result, errors.New(errMsg)
    }
    return result, nil
}
</code></pre>

<p>I have create a pipline and serve it into pipe.All() but there is null result return from the <code>result</code> varible.</p>

<p>I want to return following object in <code>result</code></p>

<pre><code>{ "_id" : ObjectId("57f73573d6e0ac1a9f2ab346") , "counts" : [ { "name" : "ubuntu", "value" : 1 }, { "name" : "linux", "value" : 14 } ] }
</code></pre>