javascript - Sum Up for each element of Collection.find() -

i try sum specific column of datapoints collection fits specific query.

getclickstotalcampaign: function () {     var docs = datapoints.find({campaign: this._id, influencer: meteor.userid()});             var clicks = 0;             for(var = 0; i< docs.length; i++) {                 clicks += parseint(docs[i].clicks);             }             return clicks;     }, 

i wrong return of datapoints.find beeing array of objects? length of null, when query on mongo entrys back. @edit here data schema:

schemas.datapoints = new simpleschema({      influencer: {         type: string,         label: "influencer id"     },     advertiser: {         type: string,         label: "advertiser id"     },     campaign: {         type: string,         label: "campaign id"     },     amount: {         type: number,         label: "amount"     }     }); 

use aggregation framework can use $match pipeline operator filter collection on campaign , influencer. $group pipeline step groups input documents filter , applies accumulator expression $sum group total documents count.

your pipeline this:

var datapoints = new mongo.collection('datapoints'); var pipeline = [     {         "$match": {             "campaign": this._id,              "influencer": meteor.userid()         }     },     {         "$group": {             "_id": null,             "count": {"$sum": "$amount"}         }     } ]; var result = datapoints.aggregate(pipeline).fetch(); var count = result[0].count; 

you can add meteorhacks:aggregate package implement aggregation in meteor:

add app with

meteor add meteorhacks:aggregate 

since package exposes .aggregate method on mongo.collection instances, can call method result array document has count field. example

if (meteor.isserver) {     var datapoints = new mongo.collection('datapoints');     meteor.methods({         getclickstotalcampaign: function () {             var pipeline = [                 {                     "$match": {                         "campaign": this._id,                          "influencer": meteor.userid()                     }                 },                                   {                     "$group": {                         "_id": null,                         "count": {"$sum": "$amount"}                     }                 }             ];             var result = datapoints.aggregate(pipeline);             return result[0].count;         }     });  }  if (meteor.isclient) {     setinterval(function () {         meteor.call('getclickstotalcampaign', updatecounter);     }, 1000 * 10);      function updatecounter(err, count) {         console.log("this new count: ", count)     } }