ratpack-mongo-changestreams basic demo app

Basic HTTP reactive application that uses Ratpack, MongoStreams and Server-sent events to send notifications to the front-end when a Document is updated in the MongoDB Collection.

We use a DevExtreme DataGrid component to provide a simple HTMl page to show and edit the data, this DataGrid uses a custom DataSource that fetches data from a Back-end endpoint that implements the required logic to query data from a MongoDB collection, parametrized by a DevExtreme loadOptions object.

Requirements

• MongoDB
• Java 8+
• [Optional] Moonshine-IDE

1. Database server setup

Option 1: VirtualBox Vagrant setup

• Download and install VirtualBox.
• Download and install Vagrant.
• Open a command line and change directory to the base path of this project.
• Execute the vagrant up command, once the process completes an Ubuntu-MongoDB virtual machine will be running.
• Continue to step 2.

Option 2: Mongo DB local installation

Click to expand!

Install MongoDB

Ubuntu

https://docs.mongodb.com/manual/tutorial/install-mongodb-on-ubuntu/.

Windows

https://docs.mongodb.com/manual/tutorial/install-mongodb-on-windows/.

install mongosh as a separate package.
Install MongoDB tools (mongoimport).

Add the path to mongoDB files to windows PATH In my case it was
C:\Program Files\MongoDB\Server\5.0\bin\
C:\Program Files\MongoDB\Tools\100\bin\

It wasn't required to add mongosh app to the windows PATH variable, but it was installed on this directory:
C:\Users\HP\AppData\Local\Programs\mongosh

Start mongoDB as a replica

Stop any mongodb server instance.

Create data directory and Start a replica instance in the default port 27017

Run the following commands to set up a simple, single-node replica set (for testing purposes).

Windows

mkdir C:\mongodb\data
mongod --replSet rs0 --dbpath "C:\mongodb\data"

Ubuntu

mkdir -p /mongodb/data
mongod --replSet rs0 --dbpath /mongodb/data

Connect (in a different terminal) using mongosh and initialize the replica

mongosh mongodb://<MONGODB_SERVER_IP>:27017/test
rs.initiate()

Import test collection

Import the grades collection from the file vagrant/grades.json into the test database like this:

mongoimport --db test --collection grades --drop --file grades.json

2. Run the project

Once the mongodb server is running you can continue and run this project

Using the Gradle wrapper

Ubuntu

./gradlew run

Windows

gradlew.bat run

From Moonshine IDE

Open the project in Moonshine with File > Open/Import Project or by double-clicking on ratpack-push.javaproj. Project > Run Gradle Command. This will run the default command gradle clean runApp.

The following endpoints are available for testing:

1. GET /api/grades: Receives a DevExtreme loadOptions object as a request parameter. Can be used to test DevExtreme components.

2. (GET, POST, PUT, DELETE) /api/grades: this endpoint exposes a basic CRUD functionality.

3. GET /grades/stream: This endpoint uses mongo Change Streams to respond with a Server-sent event when any operation (insert, update, delete) is performed on the Grades collection (similar to what we have in the Ratpack back-end demo app).

4. GET /frontend: This is an endpoint for testing the back-end endpoints. It responds with an HTML page that displays a list of Grades and dynamically updates the table when a notification (Server-sent event) is received.

3. Update the collection using mongosh

Any modification/insertion into the restaurants collection will trigger a server-sent event in the Ratpack application.

Connect to mongosh
mongosh mongodb://<MONGODB_SERVER_IP>:27017/test

Then within mongosh To update a single document:

db.grades.updateOne(
   { quizScore: { $gte: 90 } },
   [{ $set: { examScore: { $round: [ { $multiply: [ { $rand: {} }, 100 ] }, 2 ] } } }]
);

To update multiple documents:

try {
   db.grades.updateMany(
      { examScore: { $lte: 25 } },
      [{ $set: { examScore: { $round: [ { $multiply: [ { $rand: {} }, 100 ] }, 2 ] } } }],
   );
} catch (e) {
   print(e);
}

References

• https://www.mongodb.com/blog/post/an-introduction-to-change-streams