Adding an element to a list in a MongoDB Document using Java

Question

I am a little confused as to how to add an element to an array in an exisiting mongodb document, or why my results are not showing properly and how I expect.

There is only one document in the collection and will only ever be one. The mongo document looks like when I do a db.collection-name.find.pretty() command in a mongo session on the command line:

{
    "_id" : ObjectID("1234567890"),
    "details" : {
        ...
    },
    "calculations" : [
        {
            "count" : 1,
            "total" : 10,
            "mean" : 2.5
        },
        {
            "count" : 2,
            "total" : 20,
            "mean" : 6.4
        }
    ]
}

I want to add another object to the calculations list.

The Java code I am running is based upon THIS example:

// Get the database and collection
MongoDatabase database = mongo.getDatabase(dataBaseName);
MongoCollection<Document> collection = database.getCollection(collectionName);
Document document = collection.find().first(); // will only ever be one document 

// The object comes in as a Map
Map<String, Object> incomingMap = new HashMap<>();
incomingMap.put("count", 3);
incomingMap.put("total", 4);
incomingMap.put("mean", 7.9);
// convert to a Document
Document newDocument = new Document();
incomingMap.forEach((k, v) -> {
        newDocument.append(k, v);
});

// append this to the collection - this is where I am confused
// for this example just hardcoding the _id value for simplicity
collection.updateOne(new Document("_id", "1234567890"), Updates.push("calculations", newDocument));

However when I do a System.out.println(collection.find().first()) in the code after this or db.collection-name.find.pretty() in a mongo session the new document has not been added. There are no errors thrown and completes fine.

What I am wondering is

Is the line collection.updateOne(new Document("_id", "1234567890"), Updates.push("calculations", newDocument)); correct?
Has it been added but not been saved - if so how do I save?
Can I do this at a document level, for example document.update(new Documen(Updates.push("calculations", newDocument)); or similar?
I have also tried collection.findAndUpdateOne(new Document("_id", "1234567890"), Updates.push("calculations", newDocument)); with the same result
Is how I am getting/hardcoding the document ID incorrect?

So I have added in a way of getting the document ID instead of hard coding and it works?! Either I had a typo in my ID value or removing my print statement I had for debugging has made it work. If anyone could confirm that what I have done is correct that would be good so I can marked it as answered! — KitsonRis
– KitsonRis, Commented Feb 9, 2020 at 12:58

Valijon · Accepted Answer · 2020-02-09 15:56:38Z

1

You have filter condition issue (your _id is ObjectId type)

new Document("_id", ObjectId("1234567890"))`

Always make sure your documents updated correctly. Look code fagment:

UpdateResult result = collection.updateOne(filter, update);
log.info("Update with date Status : " + result.wasAcknowledged());
log.info("Nº of Record Modified : "   + result.getModifiedCount());

https://api.mongodb.com/java/3.1/com/mongodb/client/result/UpdateResult.html

answered Feb 9, 2020 at 15:56

Valijon

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