Sum aggregation for MongoDB via NodeJS

Question

Before I begin, I want to state that no other answers regarding similar questions applied to this one. First consider the following JSON code

  "_id": "1412302013-01-20,11:32:22" 
  "display": [
    {
      "Name": "LOG-11-05-SH-O1.mp4",
      "Type": "Startup",
      "Count": 2,
      "Detail": [
        {
          "Start": "2013-01-20,11:32:22",
          "End": "2013-01-20,11:32:30"
        },
        {
          "Start": "2013-01-20,11:32:22",
          "End": "2013-01-20,11:32:30"
        }
      ]
    },
    {
      "Name": "PUR-12-47-SH-X3.mp4",
      "Type": "Movie",
      "Count": "2",
      "Detail": [
        {
          "Start": "2013-01-20,11:32:22",
          "End": "2013-01-20,11:32:30"
        },
        {
          "Start": "2013-01-20,11:32:22",
          "End": "2013-01-20,11:32:30"
        }
      ]
    },

The ID is basically a combination of a license plate number concatted with a time stamp. What I am trying to do is aggregate the sum for "Count", where the "Name": "LOG-11-05-SH-O1.mp4".

I could not even get simple sums to be aggregated, so trying to aggregate this sum has been impossible. When running my script in NodeJS, I either get undefined or [object Object].

I have no clue what is going wrong as I've been following various online examples.

After trying to use parvin's answer below, I am still getting undefined:

collection.aggregate([
    {$match : {"display.Name" : "LOG-11-05-SH-O1.mp4"}},
    {$unwind : "$display"},
    {$group : {_id : "$_id", 
               name : {$first : "$display.Name"}, 
               total : {$sum : "$display.Count"}
              }   
    }], function(err, result) {
    console.log("Aggregation: " + result.total);
});

I've been trying to format the code like these docs.

JohnnyHK · Accepted Answer · 2014-01-22 13:43:16Z

3

The aggregate callback's result parameter is an array, not a single value. You can see this if you just dump out result:

console.log(result);

So to access total of the first doc in the array:

console.log(result[0].total);

But that's going to be 0 because Count in your doc is a string, not a number. You can't $sum strings.

Because you also only want the total for only the "Name": "LOG-11-05-SH-O1.mp4" elements, you need to add another filter after your $unwind:

collection.aggregate([
    {$match : {"display.Name" : "LOG-11-05-SH-O1.mp4"}},
    {$unwind : "$display"},
    {$match : {"display.Name" : "LOG-11-05-SH-O1.mp4"}},
    {$group : {_id : "$_id", 
               name : {$first : "$display.Name"}, 
               total : {$sum : "$display.Count"}
              }   
    }], function(err, result) {
        console.log(result);
});

edited Jan 22, 2014 at 13:43

answered Jan 21, 2014 at 13:57

JohnnyHK

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7 Comments

krikara Over a year ago

Interesting... so $sum doesn't actually give me a sum, forcing me to create a loop in order to add up all the array values.

JohnnyHK Over a year ago

@krikara The right way to fix this is to change your data so that Count is a number instead of a string.

krikara Over a year ago

Yeah I just changed Count to an actual number. But it still isn't a sum, so I still need the loop. I think that is what confused me the most, because in the Mongo shell it was actually a sum. But NodeJS just takes each individual value and stores it in the array.

krikara Over a year ago

Actually, I still didn't reach my goal. The aggregation code "sums" all the Count under display, but I was looking for the sum of the all the Count where "Name": "LOG-11-05-SH-O1.mp4".

JohnnyHK Over a year ago

@krikara See updated answer. You need to $match again after the $unwind for that.

|

Parvin Gasimzade · Accepted Answer · 2014-01-21 09:27:25Z

1

You can use the following query to find the total count for the Name = "LOG-11-05-SH-O1.mp4". This is the javascript example, you have to convert it to node.js

db.collection.aggregate(
    {$match : {"display.Name" : "LOG-11-05-SH-O1.mp4"}},
    {$unwind : "$display"},
    {$group : {_id : "$_id", 
               name : {$first : "$display.Name"}, 
               total : {$sum : "$display.Count"}
    }}
)

edited Jan 21, 2014 at 9:27

answered Jan 21, 2014 at 9:11

Parvin Gasimzade

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2 Comments

krikara Over a year ago

This is not working for me, I'm getting the following error. TypeError: object is not a function. I've also tried adding function(err, count){ as well as putting it into array format, but it still doesn't seem to work.

krikara Over a year ago

I updated my JSON above. The aggregation code "sums" all the Count under display, but I was looking for the sum of the all the Count where "Name": "LOG-11-05-SH-O1.mp4". Would this be possible?

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