MongoDb 节点 js 带有更改流的实时通知

Question

In my web application i have followers and notifications. The problem is how to get to the list of users and report changes of some document like changed price, or user created one more property etc.. So i can use change streams to watch for changes inside collection.

Property.watch().
on('change', async data => {
  let prop = await Property.findById(data.documentKey._id);
  let user = await Follow.findOne({userId: prop.user._id});

  // After that find all followers then 
  user.followers.forEach(foll => {
    await Notification.create({
      ...
    })
  })
});

This code looks crazy to me, I mean even with some validations etc.. this is again overkill.

Maybe better approach is some logic inside controller, but how i can first return response to user after he successfully created or updated document and then run some function where i can find all users on followers list and create notifications for them?

What you guys think? There is not much examples and solutions for notification system, is there any resource that can be helpful

Answer 1

Change streams support filtering and other functionality.

Answer 2

So basically i ended up with code like this. Inside update and create controller i'm creating user activity and then i'm watching that model.

Activity.watch().on('change', async (data) => {
  const { fullDocument } = data;
  const followers = await Follow.findOne({ user: fullDocument.user});
  if(!followers) return;

  let doc = [];

  followers.followers.forEach(follower => {
    let obj = {};

    obj.senderId = fullDocument.user;
    obj.receiverId = follower;
    obj.message = fullDocument.activityMessage;

    doc.push(obj);
  })

  try {
    await Notification.insertMany(doc);
  } catch(err) {
    console.log(err);
  }
})