How to know in mongodb that certain data has changed?

Question

MongoDB

How to know in mongodb that certain data has changed?

Answer 1

In mongo, since version 3.6. there is such a thing as Change Streams . The bottom line is that you in the code, after connecting to the database, subscribe to data changes in a special way. For example, if you want to track changes in the Books collection:

const collection = db.collection('Books');
const changeStream = collection.watch();
changeStream.on('change', event => {
  // event — см. типы событий: https://docs.mongodb.com/manual/reference/change-events/
});

An important point: Change Streams only works if the MongoDB server is running in cluster mode, not how it starts by default. A few details on how to do this: https://habr.com/en/post/335772/ (see the "Configuring and adding servers to the Replica Set" section).