summation of two columns in Aggregate Method

Question

I am using mongodb Aggregate query. My db is like this:

{
  \"_id\" : ObjectId(\"5a81636f017e441d609283cc\"),
  \"userid\": \"123\",
  page : \'A\',
  newpage: \         


        

Answer 1

Use $facet pipeline stage to process multiple aggregation pipelines within a single stage on the same set of input documents. In your case you need to aggregate the counts separately then join the two results and calculate the final aggregates.

This can be demonstrated by running the following pipeline:

db.collection.aggregate([
    { "$match": { "userid": "123" } },
    {
        "$facet": {
            "groupByPage": [
                { "$unwind": "$page" },
                { 
                    "$group": {
                        "_id": "$page",
                        "count": { "$sum": 1 }
                    }
                }
            ],   
            "groupByNewPage": [
                { "$unwind": "$newpage" },
                { 
                    "$group": {
                        "_id": "$newpage",
                        "count": { "$sum": 1 }
                    }
                }
            ]
        }
    },
    { 
        "$project": {
            "pages": {
                "$concatArrays": ["$groupByPage", "$groupByNewPage"]
            }
        }
    },
    { "$unwind": "$pages" },
    { 
        "$group": {
            "_id": "$pages._id",
            "count": { "$sum": "$pages.count" }
        }
    },
    { "$sort": { "count": -1 } }
], function(error, data){
    if (error) {
        console.log(error);
    } else {
        console.log(data);
    }
)