Why does Spring Data MongoDB not expose events for update…(…) methods?

Question

It appears that the update for mongoOperations do not trigger the events in AbstractMongoEventListener.

This post indicates that wa

Answer 1

You can listen to database changes, even the changes completely outside your program (MongoDB 4.2 and newer).

(code is in kotlin language. same for java)

@Autowired private lateinit var op: MongoTemplate

@PostConstruct
fun listenOnExternalChanges() {
    Thread {
        op.getCollection("Item").watch().onEach {
            if(it.updateDescription.updatedFields.containsKey("name")) {
                println("name changed on a document: ${it.updateDescription.updatedFields["name"]}")
            }
        }
    }.start()
}

This code only works when replication is enabled. You can enable it even when you have a single node:

Add the following replica set details to mongodb.conf (/etc/mongodb.conf or /usr/local/etc/mongod.conf or C:\Program Files\MongoDB\Server\4.0\bin\mongod.cfg) file

replication:
  replSetName: "local"

Restart mongo service, Then open mongo console and run this command:

rs.initiate()