MongoDB - Many counts using an array

Question

How to make many counts using an array as input in Mongoose, and return an array

I am trying to use the code below but it is not working, list2 is returning as empty.

list = ['Ann', 'Bob', 'John', 'Karl'];
list2 = [];

for(let i = 0; i < list.length; i++) {
    Clients.count({name: list[i]}, function(err, doc){
        list2.push(doc);
    })
}
return list2

Clients.count() is an asynchronous function. return list2 will be executed before all the db queries are completed, so that count in list2 will not accurate when you consume it. You better learn how to handle asynchronous code via callbacks or promises. — Nidhin David
– Nidhin David, Commented Jan 21, 2017 at 16:17
If you get the data in form of array of objects like this [ {name:'Ann',Count:1},{name:'Bob',Count:3},{name:'John',Count:5} ], Will that be ok for you? — Tarush Arora
– Tarush Arora, Commented Jan 21, 2017 at 16:21

chridam · Accepted Answer · 2017-01-21 17:11:40Z

3

You could run an aggregation pipeline as follows:

list = ['Ann', 'Bob', 'John', 'Karl'];
list2 = [];
Clients.aggregate([
    { "$match": { "name": { "$in": list } } },
    {
        "$group": {
            "_id": "$name",
            "count": { "$sum": 1 }
        }
    },
    {
        "$group": {
            "_id": null,
            "list2": {
                "$push": {
                    "name": "$_id",
                    "count": "$count"
                }
            }
        }
    }
]).exec(function(err, results) {
    list2 = results[0].list2;
    console.log(list2);
});

answered Jan 21, 2017 at 17:11

chridam

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Med Lazhari · Accepted Answer · 2017-01-21 16:28:22Z

2

const async = require('async');

var list = ['Ann', 'Bob', 'John', 'Karl'];

async.map(list, function(item, callback) {
    result = {};
    Clients.count({name: item}, function(err, data) {
        result[item] = data || 0;
        return callback(null, result);
    });
}, function(err, data) {
    console.log(data);
});

answered Jan 21, 2017 at 16:28

Med Lazhari

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Community · Accepted Answer · 2017-05-23 11:52:55Z

0

Here's another way based on Med Lazhari's answer

const async = require('async');

var list = ['Ann', 'Bob', 'John', 'Karl'];

var counting = function (item, doneCallback) {
    var query = Clients.count({name: item});
    query.then(function (doc) {
      return doneCallback(null, doc);
    });  
  };

async.map(list, counting, function(err, data) {
    console.log(data);
});

edited May 23, 2017 at 11:52

CommunityBot

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answered Jan 21, 2017 at 17:22

rafaelcb21

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