mashariqk / mongocs

Change streams demo for mongodb using java async client

MongoDB Changestream demo

This poc project can be used to demonstrate the change stream concept and how it can be used to create an audit trail if needed. The application is designed to only receive updates of customers with the birth month specified in the property watch.cursor.month. It will default to January if no month is provided

Tech

• Java 1.8
• Mongo DB 4.2.3
• Gradle 5.6.4

Installation

From the root of the project run the following commands:

mkdir -pv data/db
mongod --dbpath ./data/db --replSet "rs"

if you get address already in use error then run the following commands in a new shell

mongo
use admin
db.shutdownServer()

Then run the previous commands before running the following.

Then in a separate shell tab, run:

mongo

After the rs:PRIMARY> prompt (or just > in the first run) appears, run:

rs.initiate()

For the first run the output will be something like

{
	"info2" : "no configuration specified. Using a default configuration for the set",
	"me" : "localhost:27017",
	"ok" : 1,
	"$clusterTime" : {
		"clusterTime" : Timestamp(1586447207, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	},
	"operationTime" : Timestamp(1586447207, 1)
}

For subsequent runs it may give an error like below which can be ignored

{
	"operationTime" : Timestamp(1586447350, 1),
	"ok" : 0,
	"errmsg" : "already initialized",
	"code" : 23,
	"codeName" : "AlreadyInitialized",
	"$clusterTime" : {
		"clusterTime" : Timestamp(1586447350, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

Open a new terminal window and navigate to the root of the project. Then run

mongo src/main/resources/createCustomers.js

Completing these steps will start the mongo db and a steady stream of data getting inserted in the database test and in collection customers with random first and last names and a random birth month. Once this setup is done start the spring boot app with the following command

gradle bootRun

The app will now start receiving the updates of users with the birthday month as specified. The createCustomers.js file is only inserting records, to see an update a query like below can be executed in mongo shell

db.customers.update({"firstName":"fname3195"},{$set: {"lastName":"uofname2376"}});