Java and MongoDB: forEach(Block) is ambiguous

Question

I'm trying to extend the Azure Java / MongoDB simple example with a filter from mongodb docs while getting my head around functional Java. The below code is throwing errors

        MongoDatabase database = mongoClient.getDatabase("my-db");
        Document queryResult = collection.find(Filters.eq("fruit", "apple")).first();

        Bson filter = Filters.and(Filters.eq("param", 2293), Filters.eq("param1", 202));
        final Document queryResult2 = collection.find(filter).forEach(doc -> 
        System.out.println(doc.toJson()));

is giving me the following error

The method forEach(Block<? super Document>) is ambiguous for the type FindIterable<Document>",

I have looked at this answer and tried various things including below but my lack of experience with forEach is obvious!

           //cannot convert from void to document error
            Document queryResult2 = collection.find(filter).forEach((Block<? super Document>) doc -> System.out.println(doc.toJson()));

            //cannot convert from void to document error
            final Document queryResult2 = collection.find(filter).forEach((Consumer<? super Document>) (Document document) -> {
                System.out.println(document.toJson());
            });

All help/tips appreciated

What is the version of your Java driver? Check the API docs for your driver version. — prasad_, Aug 29 '22 at 13:51
it was 3.4.2, after your question I updated to 3.12.11 but the error remains — user1843591, Aug 29 '22 at 14:00
collect all documents that match my filter and write them as a consolidated file to a file store — user1843591, Aug 29 '22 at 14:03
@user1843591 Remove the left hand side of the assignment i.e. `final Document queryResult2 =` — akg179, Aug 29 '22 at 14:11
For your driver version try this: `collection.find(filter).cursor()` returns a `MongoCursor` (you can use its methods for iteration). — prasad_, Aug 29 '22 at 14:26

score 1 · Accepted Answer · answered Aug 29 '22 at 14:11

There are two errors here:

Document queryResult2 = collection.find(filter).forEach((Block<? super Document>) doc -> System.out.println(doc.toJson()));

forEach has a return type of void, it doesn't return anything. So the assignment is wrong. That's why you get cannot convert from void to document error

Secondly Document, represents a single document, not a collection of documents. So the assignment to simply a Document object is wrong as well.

Try something like this:

List<Document> documents = collection.find(filter).map(doc -> doc).into(new ArrayList<Document>());

Here's the link to the forach and map Mongodb documentation.

Java and MongoDB: forEach(Block) is ambiguous

1 Answers1