Java MongoDB: updating one item within an object array

I dug around for a little while and actually found a solution for this. It comes in the form of a positional operator:

https://docs.mongodb.org/manual/reference/operator/projection/positional/

I also read this thread related to positional operators and how to update elements of an array here:

How to update value of specific embedded document, inside an array, of a specific document in MongoDB?

com.mongodb.DBCollection collection = mongoTemplate.getDb().getCollection("person");
            ObjectId _id = new ObjectId("2984");
            ObjectId photos_id = new ObjectId(10);

            BasicDBObject query = new BasicDBObject();
            query.put("_id", _id);
            query.put("photos._id", photos_id);

            BasicDBObject data = new BasicDBObject();
            data.put("photos.$.distributor", "Pixel Studios");

            BasicDBObject command = new BasicDBObject();
            command.put("$set", data);

            collection.update(query, command);

It's much easier to modify the object you get from the database on the client side.
I am assuming here that the documents inside photos are ordered by the _id, if it's not the case you'll have to search inside the array, and thus have a few more steps. First, here is how you do this in the mongo shell (JavaScript), but this should not be much different in Java:

> v = db.ppl.find({_id: "2894"}).next();
{
    "_id" : "2894",
    "_class" : "com.foo.Person",
    "name" : "Pixel Spacebag",
    "photos" : [
        {
            "_id" : 10,
            "amount" : "100"
        },
        {
            "_id" : 11,
            "amount" : "200"
        }
    ]
}
> v.photos[0]
{ "_id" : 10, "amount" : "100" }
> v.photos[0].distributor = "pixel studios"
> v.photos[0]
{ "_id" : 10, "amount" : "100" }
> v.photos[0].distributor = "pixel studios"

> db.ppl.update({_id:"2894"}, {$set : {"photos": v.photos}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.ppl.findOne()
{
    "_id" : "2894",
    "_class" : "com.foo.Person",
    "name" : "Pixel Spacebag",
    "photos" : [
        {
            "_id" : 10,
            "amount" : "100",
            "distributor" : "pixel studios"
        },
        {
            "_id" : 11,
            "amount" : "200"
        }
    ]
}

So, where I am using . for assignment you'll have to use the appropriate get or set method with possible casting for the right type.

The following code is the Java equivalent for the JS I posted above:

Document example = new Document("_class", "com.foo.Person")
                .append("_id", "2894")
                .append("name", "Pixel Spacebag");

        List<Document> photos = new ArrayList<Document>();
        photos.add(new Document("_id", 10).append("amount", "100"));
        photos.add(new Document("_id", 11).append("amount", "200"));

        example.append("photos", photos);
        collection.insertOne(example);

        FindIterable<Document> res = collection.find(new Document("_id", "2894"));
        Document temp = res.iterator().next();
        List<Document> photosDoc = (List<Document>) temp.get("photos");
        Document docToUpdate = photosDoc.get(0);
        docToUpdate.append("distributor", "pixel studios");
        photosDoc.set(0, docToUpdate);
        collection.updateOne(new Document("_id", temp.get("_id")),
                new Document("$set", new Document("photos", photosDoc)));

        /* Check that everything worked */
        res = collection.find(new Document("_id", "2894"));
        Document updatedDocument = res.iterator().next();
        System.out.println(updatedDocument);
        /* outputs:
         Document{{_id=2894, _class=com.foo.Person, name=Pixel Spacebag, photos=[Document{{_id=10, amount=100, distributor=pixel studios}}, Document{{_id=11, amount=200}}]}}
         */