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I am building a social media and one of the features I have is the ability to follow other users and have their posts show up on a home page, much like an Instagram feed. I have an endpoint that loops through all the users you are following and gets the post that are rated for your age, sorts them and puts them in an array.

router.get("/following", auth, async (req, res) => {
  try {
    const user = await User.findOne({ firebaseUID: req.authId });

    const dob = dayjs(user.dob.toISOString().split("T")[0]);
    const currentDate = dayjs(new Date().toISOString().split("T")[0]);

    const age1 = currentDate.diff(dob, "year");

    let posts = [];
    for (let i = 0; i < user.following.length; i++) {
      posts.push(
        await Post.find({
          userID: user.following[i].user,
          age: { $lte: age1 },
        })
      );
    }

    posts = [].concat.apply([], posts);

    posts = _.sortBy(posts, "date").reverse();

    res.json(posts);
  } catch (err) {
    console.error(err.message);
    res.status(500).json({ msg: "Server Error" });
  }
});

The user schema looks like this

const UserSchema = new Schema({
  firebaseUID: {
    type: String,
    required: true,
  },
  name: {
    type: String,
    required: true,
  },
  username: {
    type: String,
    required: true,
    unique: true,
  },
  avatar: {
    type: String,
  },
  dob: {
    type: Date,
    default: Date.now,
    required: true,
  },
  slug: {
    type: String,
  },
  following: [
    //array of user IDs
    {
      user: {
        type: Schema.Types.ObjectId,
        ref: "users", //here so we know which lieks came from which users
      },
    },
  ],

  followers: [
    //array of user IDs
    {
      user: {
        type: Schema.Types.ObjectId,
        ref: "user", //here so we know which lieks came from which users
      },
    },
  ],
});

The problem is that I am trying to add infinite scroll pagination to the front end that will start by getting the first 15 posts and then get the next 15 and so on from endpoints that provide this.

What would the best way to do this be? For other routes, I have used .skip() and .limit(). I could split the array of posts up right before I send it as a response, but is there a way to do without getting all the posts as this would be taxing if you're following 100s of people with 1000s of posts.

I would need to loop through all the users you are following and get all their posts in line with your age rating but only get the first 15 sorted in date order from newest to oldest. Is there a mongoose function that I could use or would the best way be to split the array of posts?

Thank you.

Thomas Pritchard
  • 36
  • 3
  • Currently, you are making one detabase request per post, in a `for` loop. If you fetch 50 posts, that's 50 database requests. _That_ is taxing. You could fetch all 50 posts in one single requests by doing `await Post.find({ userID: { $in : [ id1, id2, id3, id4 ] }, age: { $lte: age1 },})`. Also, to speed up the queries, add `.lean()` which will return simple JSON instead of a Mongoose documents collection, and also `.exec()` which returns a true Promise, not a thenable. `const docs = await find(conditions).lean().exec();` – Jeremy Thille Aug 25 '21 at 13:13
  • An even better solution would be to populate `user.following` : `const user = await User.findOne({ firebaseUID: req.authId }).populate("following").lean().exec();`, and bam, immediately you get all full posts ready and you can `res.json(user.following)`. – Jeremy Thille Aug 25 '21 at 13:16
  • @JeremyThille Thank you for your response, using ```const user = await User.findOne({ firebaseUID: req.authId }).populate("following").lean().exec(); ``` outputs an array of object ```[{ "_id": "6123ff3c6dd36945c0da5384", "user": "6113ee7005f83235181247d1"}, {"_id": "6124ce7945ccbb481c79823d", "user": "60f3f2c51a69eb0960f77f51"}, { "_id": "6124ce8145ccbb481c798255", "user": "610d51b6027393363812e13d"}, { "_id": "6124d38545ccbb481c79834c", "user": "60fb217835afcc26c8568bdf" }]``` How would I get the posts from this? – Thomas Pritchard Aug 25 '21 at 13:52
  • I believe `ref: "users"` should instead be `ref: "User"`, then your population should work – Jeremy Thille Aug 25 '21 at 14:06
  • Or maybe `following : [ this ]`, I just found it here : https://stackoverflow.com/questions/24964914/can-a-mongo-model-self-reference – Jeremy Thille Aug 25 '21 at 14:08

0 Answers0