Cosmos Change Feed Demo App

Simple Demo For Cosmos Change Feed while using MongoDB API

MongoDB natively has ChangeStream that is synonomous with Change Feed Of CosmosDB.

When using CosmosDB with MongoDB API, We can just use MongoDB Change Stream directly. We just have to be aware, the entire MongoDB ChangeStream functionalities may not be supported by CosmosDB. Check Limitations

Demo APP

In the Demo App, there are two Collections Employee & DuplicateEmployee. The App listens for ChangeFeed/ChangeStream messages on Employee Collection and inserts/updates the same Document into DuplicateEmployee Collection.

PreReqs

1. Access To Azure CosmosDB
2. Ensure MongoDB APi 3.6 version is used / enabled in Azure Portal
3. Ensure MongoDB Aggregation Pipeline is enabled in Azure Portal
4. Create New DB / Use Existing DB
5. Create two Collections named Employee and DuplicateEmployee
6. Rename src/main/resources/sample_application.properties to application.properties
7. Modify src/main/resources/application.properties to update MONGO URI and DB Name specific to your azure account

Reactive Java

Reactive programming is a programming paradigm that deals with asynchronous data streams (sequences of events) and the specific propagation of change, which means it implements modifications to the execution environment (context) in a certain order. More Details Being Spring boot project uses Spring Reactive. This is used via below dependency

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb-reactive</artifactId>
    <version>2.2.6.RELEASE</version>
</dependency>

Execute

1. This is a typical Spring Boot APP. Run com.gauri.cosmosdemo.Main class.
2. Using Azure portal add a new Document to Employee Collection as per below structure. This App would have listened to changes in Employee Collection and inserted/updates a document in DuplicateEmployee Collection.

{
    "_id": 4,
    "name": "Gauri",
    "department": "IT",
    "designation": "Engg"
}

EmployeeChangeFeedListener

EmployeeChangeFeedListener.java sets up and subscribes to the ChangeStream of Employee Collection and acts to process the change (ie) inserting / updating same document in DuplicateEmployee Collection.

Rest Endpoints For Testing

Few Rest Endpoints are powered by Demo App via TestServiceController.java Once Server is running, base path of the endpoints are http://localhost:8080/cosmosdemo/test

Path	Type	Functionality
http://localhost:8080/cosmosdemo/test/allEmployees	GET	Gets all Documents from Employee Collection
http://localhost:8080/cosmosdemo/test/statusChangeFeedEmployee	GET	Gets the status of Employee Change Feed Subscription that informs, if the subscription is active
http://localhost:8080/cosmosdemo/test/terminateChangeFeedEmployee	GET	Terminates the Employee Change Feed Subscription
http://localhost:8080/cosmosdemo/test/insertEmployee	POST { "_id": 4, "name": "Gauri", "department": "IT", "designation": "Engg" }	Insert a document into Employee Collection