Node js + Mongodb better way to select count of specific documents

Question

What would be the better way to select count of users

Will the JavaScript filtering code work fine if the number of users increases?

Using multiple mongodb requests

 const db = fastify.mongo.db;
 const users_collection = await db.collection('users');

 let users = {
     registered: {
         count: null,
         typed_count: {
             vk: null,
             ok: null,
             google: null,
             oneclick: null,
         },
     },
 };

 users.registered.count = await users_collection.countDocuments();
 users.registered.typed_count.vk = await users_collection.countDocuments({ 'social.vk': { $exists: true } });
 users.registered.typed_count.ok = await users_collection.countDocuments({ 'social.ok': { $exists: true } });
 users.registered.typed_count.google = await users_collection.countDocuments({ 'social.google': { $exists: true } });
 users.registered.typed_count.oneclick = await users_collection.countDocuments({ social: { $exists: false } });

Using one mongodb request and javascript filtering

 const db = fastify.mongo.db;
 const users_collection = await db.collection('users');

 let users = {
     registered: {
         count: null,
         typed_count: {
             vk: null,
             ok: null,
             google: null,
             oneclick: null,
         },
     },
 };

 const data = await (await users_collection.find()).toArray();
 users.registered.count = data.length;
 users.registered.typed_count.vk = data.filter((obj) => obj.social && obj.social.vk).length;
 users.registered.typed_count.ok = data.filter((obj) => obj.social && obj.social.ok).length;
 users.registered.typed_count.google = data.filter((obj) => obj.social && obj.social.google).length;
 users.registered.typed_count.oneclick = data.filter((obj) => !obj.social).length;

namar sood · Accepted Answer · 2020-08-01 21:03:27Z

1

The First Method will take more time as too many network requests are involved and

The Second Method will take too much of your server's memory (RAM) as all the documents will first be brought into the memory.

So we can reduce both time and memory by using MongoDB aggregation's $group pipeline, which will look something like this

db.collection.aggregate([
  {
    $group: {
      _id: null,
      vk: {
        $sum: {
            $cond: [{ $gt: ["$social.vk", null]}, 1, 0]
        }
      },
      ok: {
        $sum: {
          $cond: [{ $gt: ["$social.ok", null]}, 1, 0]
        }
      },
      google: {
        $sum: {
          $cond: [{ $gt: ["$social.google", null]}, 1, 0]
        }
      },
      oneclick: {
        $sum: {
          $cond: [{ $lte: ["$social", null]}, 1, 0]
        }
      },
      
    }
  }
])

Working Example

answered Aug 1, 2020 at 21:03

namar sood

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