How to use a JSON file to aggregate in MongoDB in Java?

Question

I am using the Java MongoDB driver v4.3:

implementation group: 'org.mongodb', name: 'mongodb-driver-sync', version: '4.3.1'
implementation group: 'org.mongodb', name: 'bson', version: '4.3.1'

I have my aggregation pipelines written in JSON files which are placed in the src/main/resources folder. The aggregate function only accepts a List<Bson>. After fetching the file, how do I pass it into the MongoDB method?

String fileName = "physics/test.json";
File file = new File(fileName);
MongoDatabase db = mongoClient.getDatabase(DATABASE_NAME);
MongoCollection collection = db.getCollection(collectionName);
// Convert file to List<Bson> ???
AggregateIterable sourceList = collection.aggregate(pipeline);

I don't believe there are any converters that will convert JSON to Java-based aggregation pipelines. In Atlas, there is a code converter, but this is expected to be a design-time implementation, not a run-time implementation. — barrypicker
– barrypicker, Commented Aug 19, 2021 at 17:39
The aggregate pipeline is an array of aggregation stages - and in Java this is a List of stages - each stage defined as Bson or its implementation org.bson.Document. You may want to tell what the contents of the file look like. Maybe you can read the file and convert it into the List. — prasad_
– prasad_, Commented Aug 20, 2021 at 3:30
@prasad_ I have many files which have aggregations that consists of lots of pipelines. One pipeline is like this: [{"$group":{"_id":{"segment":"$segment","invoice_id":{"$trim":{"input":"$invoice_id"}}},"qty":{"$sum":"$qty"}}}] — khateeb
– khateeb, Commented Aug 20, 2021 at 9:12
Thats native code (and its a JSON string). You may have to parse it to instances of Bson. The Document class has some methods like parse. — prasad_
– prasad_, Commented Aug 20, 2021 at 9:49

khateeb · Accepted Answer · 2021-08-23 11:35:24Z

1

This is how you do it:

import org.bson.json.JsonObject;
// ...
    
String json = """
        [{"$group":{"_id":{"segment":"$segment","invoice_id":{"$trim":{"input":"$invoice_id"}}},"qty":{"$sum":"$qty"}}}]""";

List<BsonDocument> pipeline = new BsonArrayCodec().decode(new JsonReader(json), DecoderContext.builder().build())
        .stream().map(BsonValue::asDocument)
        .collect(Collectors.toList());

MongoClient client = new MongoClient();

List<JsonObject> results = client.getDatabase("test").getCollection("test").withDocumentClass(JsonObject.class)
        .aggregate(pipeline).into(new ArrayList<>());

for (JsonObject cur: results) {
    System.out.println(cur.getJson());
}

answered Aug 23, 2021 at 11:35

khateeb

5,51916 gold badges68 silver badges124 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user2290269 Over a year ago

This will fail in case the JSON contains datetimes, because there are treated like strings not ISODate(). And it will fail if you are using constants like ISODate() because this is not a valid JSON anymore.

Collectives™ on Stack Overflow

How to use a JSON file to aggregate in MongoDB in Java?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related