Limit mongoose schema length

Question

How can I limit mongoose schema length, remove the first/oldest item from the schema when it reaches the limit and appends the new value to the schema?

const mongoose = require("mongoose");

const Post = new mongoose.Schema({
  User: { type: mongoose.Schema.Types.ObjectId, ref: "User", required: true },
  Posts: { type: Object }
  Date: { type: Date, default: Date.now }
});

As you can see above in the code, I have Posts schema, it accepts items with no limit, but let's say I want to limit it with 50 posts when a user adds more than 50 posts it should automatically delete/remove the first item and save the newest post.

So you want to create a FIFO (First in First out) data structure? — Jorge Guerra Pires, Mar 18 '20 at 16:09
hey there, are you sure this is correct ` Posts: { type: Array }`? array of what? — Jorge Guerra Pires, Mar 18 '20 at 16:25
@JorgePires an array of posts, Posts: [ { _id: xxxxxx..., postType: 2, imgurl: 'http://url-to-image', caption: 'lorem ipsum.'}, { _id: xxxxxx..., postType: 4, txt: 'lorem ipsum...'}, .... [upto 50 items] ] — Natnael A., Mar 18 '20 at 17:08

score 1 · Answer 1 · answered Mar 18 '20 at 14:51

1

Call a function after defining your model in mongoose. You should look up virtual functions in mongoose l, they get invoked after every change in you document.

answered Mar 18 '20 at 14:51

Saurabh Agrawal

162
2
13

score 1 · Accepted Answer · answered Mar 18 '20 at 18:58

1

since I couldn't find any MongoDB way of solving it. here's what I did to achieve this:

function newPost(post, limit) {
  Post.find({}, {}, { sort: { Date: 1 } }).then(resp => {
    if (resp.length < limit) {
      new Post(post).save();
    } else {
      Post.findByIdAndRemove(resp[0]._id).exec().catch(err => { throw err });
      new Post(post).save();
    }
  });
}

answered Mar 18 '20 at 18:58

Natnael A.

591
6
20

your solution does not seem to create the bubble effect, what happens to the movement between first and last? – Jorge Guerra Pires Mar 18 '20 at 19:04
Now I got it! you wanted to sort by date, but I believe the effect will be the same, no? if the order is FIFO. so it does not matter the date! – Jorge Guerra Pires Mar 18 '20 at 19:06
1

Sorry, my bad, you are right, and I saw you updated the question as well. I am glad things worked out just fine aftermath! – Jorge Guerra Pires Mar 18 '20 at 19:15

Jorge Guerra Pires · Answer 3 · 2020-03-18T17:18:19.660

Here goes my solution for String, you must adapt for your case. For the sake of simplicity, my vector is limited to 3, your case 50, just change the code!

require("./connection");

var mongoose = require("mongoose");

const PostSchema = new mongoose.Schema({
  User: String,
  Posts: [String] //since I am not familar with the notation { type: Array }, I have decided to work with something I am familiar with
});

PostSchema.virtual("posts").set(function(newPost) {
  if (this.Posts.length >= 3) {//change here the size to 50
    this.Posts.pop();
    this.Posts.unshift(newPost);
  } else {
    this.Posts.unshift(newPost);
  }
});

Post = mongoose.model("Post", PostSchema);

Post.findOne({ User: "Jorge Pires" }).then(post => {
  post.posts = "this is nice!";
  post.save();
  console.log(post);
});

//--------------------------------------------------------------
//uncomment for creating your first dataset sample
// Post.create({
//   User: "Jorge Pires",
//   Posts: ["Hey there", "I am on stack overflow", "this is nice"]
// });
//-----------------------------------------------------------

How it works?

The new elements will enter in the back, and the oldest will be removed if the vector size exceed its limit, mine 3 and yours 50. It creates the "bubble effect", as you introduce new elements, the oldest ones automatically will move to the head and be eliminated eventually.

references

Limit mongoose schema length

3 Answers3