Building a simple news feed in node + Mongodb + Redis

Question

My goal is to build a simple news feed in node.js with the help of mongodb and redis. It similar like twitter

So the scenario is pretty straight forward, once User A follow User B. Later on User's A News feed (Home page) will be shown User B's Activity like what he posted.

Schema for User

const UserSchema = new Schema({
  email: { type: String, unique: true, lowercase: true},
});



const followSchema = new Schema(
    {
        user: { type: Schema.Types.ObjectId, required: true, ref: 'User' },
        target: { type: Schema.Types.ObjectId, required: true, ref: 'User' },
    });

Currently the design of my user's schema is pretty simple, when I follow another user, I will just create the Follow Schema Object

and there is another schema, which is post schema

/* This is similar like the Tweet */
var PostSchema = new Schema({
  // Own by the user
  creator: { type: Schema.Types.ObjectId, ref: 'User' }
  body: String,
});

This schema is for user to post anything, similar like twitter posting.

Let say I have followed bunch of users

{
   user: 'me',
   target: 'draco'
},

{
  user: 'me',
  target: 'donald'
},

{
  user: 'me',
  target: 'joker'
}

and let say one of my followers, post something. How do i present it to my current news feed?

/* I'm following Joker */
app.post('/follow', (req, res, next) => {
   let follow = new Follow();
   follow.user = "me";
   follow.target = "joker";
   // Do i need to use redis to subscribe to him?
   follow.save();
})


/* Joker posted something */
app.post('/tweet',(req, res, next) => {
   let post = new Post();
   post.creator = "joker";
   post.body = "Hello my name is joker"
   post.save();
   // Do i need to publish it using redis so that I will get his activity?

});

Here's my attempt

app.get('/feed', function(req, res, next) {

     // Where is the redis part?
     User.findOne({ _id: req.user._id }, function(err, foundUser) {
        // this is pretty much my attempt :(
     })
})

When should I use redis to actually do the pub and sub? so that I could take the content of one of my followers and show it on my timeline?

Donne

You are not doing anything with your followees instead current user in query – Daly

What should I do to my followees array, should I loop each one of it? – Donne

Answer 1

I have built a social network which has a news feed, too. Here is how I did it.

---

Basically, you have 2 methods to built a newsfeed:

1. Fanout on write (push) method
2. Fanout on read (pull) method

---

Fanout on write

First, you will need another collection:

const Newsfeed = new mongoose.model('newsfeed', {
  owner: {type: mongoose.Types.ObjectId, required: true},
  post: {type: mongoose.Types.ObjectId, required: true}
});

When a user post something:

1. Get n follower
2. Push (fanout) this post to n follower

When a user get a feed:

1. Get from Newsfeed collection

Example:

router.post('/tweet', async (req, res, next) => {
  let post = await Post.create({});

  let follows = await Follow.find({target: req.user.id}).exec();

  let newFeeds = follows.map(follow => {
    return {
      user: follow.user,
      post: post.id
    }
  });
  await Newsfeed.insertMany(newFeeds);
});

router.get('/feed', async (req, res, next) => {
  let feeds = await Newsfeed.find({user: req.user.id}).exec();
});

---

Fanout on read

When a user post something:

1. Save

When a user get feed

1. Get n following
2. Get posts from n following

Example

router.post('/tweet', async (req, res, next) {
  await Post.save({});
});

router.get('/feeds', async (req, res, next) {
  let follows = await Follow.find({user: req.user.id}.exec();

  let followings = follows.map(follow => follow.target);

  let feeds = await Post.find({user: followings}).exec();
});

---

You don't need Redis or pub/sub to implement a newsfeed. However, in order to improve the performance, you may need Redis to implement some kind of cache for this.

For more information or advance technique, you may want to take a look at this.

Appanage

Hey thanks for helping! I'm just wondering where is the redis part thanks!! – Donne

Well, as I said before, you don't really need Redis or pub/sub mechanism to implement the very basic newsfeed. However, you can use Redis to implement caches to improve the performance. Do you want me to shed some light about that? – Appanage

@Appanage That would be great if you clarify the Redis part in the above chart. – Lagan

@Appanage What are the pros and cons of each methods? – Lagan

Link goes to a 404. – Gregory

Answer 2

User Schema :

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

const userSchema = new Schema({
     name:{type:String},
     email: { type: String, unique: true, lowercase: true},
  },{
    collection: 'User'
  });

var User = module.exports = mongoose.model('User', userSchema);

Follow Schema :

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var followSchema = new Schema(
    {
        follow_id: { type: Schema.Types.ObjectId, required: true, ref: 'User'  },
        leader_id: { type: Schema.Types.ObjectId, required: true, ref: 'User' }
    },{
        collection:'Follow'
    });

 var Follow = module.exports = mongoose.model('Follow', followSchema);

Post Schema :

 var mongoose = require('mongoose');
 var Schema = mongoose.Schema;

var postSchema = new Schema({
  creator: { type: Schema.Types.ObjectId, ref: 'User' }
  body: {type: String , required:true},
  created_at :{type:Date , default:Date.now}
},{
    collection:'Post'
  });

var Post = module.exports = mongoose.model('Post', postSchema);

Now Suppose you have 3 users in User collection :

{ _id: ObjectID('5a2ac68d1413751391111111') ,name:'John' , email:'[email protected]'}

{ _id: ObjectID('5a2ac68d1413751392222222') ,name:'Morgan' , email:'[email protected]'}

{ _id: ObjectID('5a2ac68d1413751393333333') ,name:'Emily' , email:'[email protected]'}

Now John Follows Morgan and Emily :

so in Follow collection there are two records

1) follow_id = John's ID and leader_id = Morgan's ID

2) follow_id = John's ID and leader_id = Emily's ID

{ 
  _id: ObjectID('5a2ac68d141375139999999'),
  follow_id : ObjectID('5a2ac68d1413751391111111'),
  leader_id : ObjectID('5a2ac68d1413751392222222')
},
  {
     _id: ObjectID('5a2ac68d1413751393333333'),
    follow_id : ObjectID('5a2ac68d1413751391111111'),
    leader_id : ObjectID('5a2ac68d1413751393333333')
  }

Now if you want to get User's Following :

app.get('/following/:user_id',function(req,res){
      var userid=req.params.user_id;
      Follow.find({follow_id:mongoose.mongo.ObjectID(userid)})
      .populate('leader_id')
      .exec(function(err,followings){
       if(!err && followings){ 
          return res.json({followings:followings});
       }
      });
});

for getting User's Followers :

   app.get('/followers/:user_id',function(req,res){
      var userid=req.params.user_id;
      Follow.find({leader_id:mongoose.mongo.ObjectID(userid)})
      .populate('follow_id')
      .exec(function(err,followers){
       if(!err && followers){ 
          return res.json({followers:followers});
       }
      });
});

npm install redis

in your app.js :

var redis = require('redis');
var client = redis.createClient();

When one user create post :

app.post('/create_post',function(req,res){

       var creator=new mongoose.mongo.ObjectID(req.body.creator);
       var postbody=req.body.body;


       async.waterfall([
          function(callback){

          // find followers of post creator

          Follow.find({leader_id:creator})
              .select({ "follow_id": 1,"leader_id":0,"_id": 0})
              .exec(function(err,followers){
                      if(!err && followers){ 
                      callback(null,followers);
                      }
              });
         },
        function(followers, callback){

          // saving the post

         var post=new Post({
            creator: creator,
            body: postbody
         });
          post.save(function(err,post){
             if(!err && post){

   // adding newly created post id to redis by key userid , value is postid

                for(var i=0;i<followers.length;i++){
                   client.sadd([followers[i].follow_id,post.id]);
                }


                 callback(null,post);
             }
         });   
      }
   ], function (err, result) {
             if(!err && result){
                return res.json({status:"success",message:"POST created"});
             }
       });
    });

Now For Getting User NewsFeed :

1) first get array of postid from redis key of userid

2) loop through postid and get post from mongo

Function for get newsfeed by userid :

app.get('/newsfeed/:user_id',function(req,res){
    var userid=req.params.user_id;
    client.smembers(userid,function(err, reply) {
        if(!err && reply){
            console.log(reply);

            if(reply.length>0){
               var posts=[];

               for(var i=0;i<reply.length;i++){
                  Post.findOne({_id:new mongoose.mongo.ObjectID(reply[i])}).populate('creator').exec(function(err,post){        
                 posts.push(post);
      });
               }

              return res.json({newsfeed:posts});

            }else{
              // No News Available in NewsFeed
            }
        }
    });

});

Here we have use redis to store [userid,array of postids] for newsfeed , but if you dont want to use redis than just use below Newsfeed Model and store user_id and post_id for newly created post and then display it.

NewsFeed Schema :

 var mongoose = require('mongoose');
 var Schema = mongoose.Schema;

var newsFeedSchema = new Schema({
  user_id: {type: Schema.Types.ObjectId, refer:'User' , required:true}
  post_id: {type: Schema.Types.ObjectId, refer:'Post' , required:true},
},{
    collection:'NewsFeed'
  });

var NewsFeed = module.exports = mongoose.model('NewsFeed', newsFeedSchema);

Helpful link for Redis : https://www.sitepoint.com/using-redis-node-js/

for Async : https://caolan.github.io/async/docs.html#

Nursemaid