How do I iterate over a MongoDB Change Stream in Spring Boot?

Question

I have read countless of articles and code examples on MongoDB Change Streams, but I still can't manage to set it up properly. I'm trying to listen to a specific collection in my MongoDB and whenever a document is inserted, updated or deleted, I want to do something.

This is what I've tried:

@Data
@Document(collection = "teams")
public class Teams{
    private @MongoId(FieldType.OBJECT_ID)
    ObjectId id;
    private Integer teamId;
    private String name;
    private String description;
}

---

import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;

import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.changestream.FullDocument;
import com.mongodb.client.ChangeStreamIterable;

import org.bson.Document;
import org.bson.conversions.Bson;

import java.util.Arrays;
import java.util.List;

public class MongoDBChangeStream {

    // connect to the local database server
    MongoClient mongoClient = MongoClients.create("db uri goes here");

    // Select the MongoDB database
    MongoDatabase database = mongoClient.getDatabase("MyDatabase");

    // Select the collection to query
    MongoCollection<Document> collection = database.getCollection("teams");

    // Create pipeline for operationType filter
    List<Bson> pipeline = Arrays.asList(
            Aggregates.match(
                    Filters.in("operationType",
                            Arrays.asList("insert", "update", "delete"))));

    // Create the Change Stream
    ChangeStreamIterable<Document> changeStream = collection.watch(pipeline)
            .fullDocument(FullDocument.UPDATE_LOOKUP);

    // Iterate over the Change Stream
    for (Document changeEvent : changeStream) {
        // Process the change event here
    }
}

So this is what I have so far and everything is good until the for-loop which gives three errors:

1. There is a red line under 'for (', which says unexpected token.
2. There is a red line under ' :', which says ';' expected.
3. There is a red line under 'changeStream)', which says unknown class: 'changeStream'.

Answer 1

First of all you should put your code inside class method, not class body. Second - ChangeStreamIterable<Document> iterator element is ChangeStreamDocument<Document> and not Document.

Summing things up:

public class MongoDBChangeStream {

    public void someMethod() {

        // connect to the local database server
        MongoClient mongoClient = MongoClients.create("db uri goes here");

        // Select the MongoDB database
        MongoDatabase database = mongoClient.getDatabase("MyDatabase");

        // Select the collection to query
        MongoCollection<Document> collection = database.getCollection("teams");

        // Create pipeline for operationType filter
        List<Bson> pipeline = Arrays.asList(
                Aggregates.match(
                        Filters.in(
                                "operationType",
                                Arrays.asList("insert", "update", "delete")
                        )));

        // Create the Change Stream
        ChangeStreamIterable<Document> changeStream = collection.watch(pipeline)
                .fullDocument(FullDocument.UPDATE_LOOKUP);

        // Iterate over the Change Stream
        for (ChangeStreamDocument<Document> changeEvent : changeStream) {
            // Process the change event here
        }
    }
}