Convert Value to JSON in Java

Hello everyone!

i am trying to use my db with java.
how do i convert the Value object to JSON?
this is my code:

public class Main {

    public static void main(String[] args) {
        String key = "API_KEY";
        String endPoint = "https://db.fauna.com/";

        try {
            FaunaClient client =
                    FaunaClient.builder()
                            .withSecret(key)
                            .withEndpoint(endPoint)
                            .build();

            Value value = client.query(
                    Map(
                            Paginate(
                                    Match(Index("all_titoli"))
                            ),
                            Lambda("X", Get(Var("X")))
                    )
            ).get();
            
        } catch (ExecutionException | InterruptedException | IOException ex) {
            System.out.println(ex.getMessage());
        }
    }

}

Hi @mpfauna,

I’m not sure I understand the question. The Value object is already in JSON format :

How to retrieve the values from a query result
That query returns the data in the form of a json object. It’s possible to convert Value class to its primitive correspondent using to methods specifying a type.

What is it you’re trying to do? And where are you hitting difficulty?

Cory

hi @Cory_Fauna

sorry, I explained myself wrong.
this is the result of the query:

{data: [{ref: ref(id = "315960375323394633", collection = ref(id = "musica", collection = ref(id = "collections"))), ts: 1637582144940000, data: {titolo: "canzone1", autore: "autore1"}}, {ref: ref(id = "315960386162524745", collection = ref(id = "musica", collection = ref(id = "collections"))), ts: 1637582155280000, data: {titolo: "canzone2", autore: "autore2"}}]}

how do i iterate over the result and view the fields?

i tried in this way:

FaunaClient client =
		FaunaClient.builder()
				.withSecret(key)
				.withEndpoint(endPoint)
				.build();

Value value = client.query(
		Map(
				Paginate(
						Match(Index("all_titoli"))
				),
				Lambda("X", Get(Var("X")))
		)
).get();

Collection<String> coll = value.asCollectionOf(String.class).get();
System.out.println(coll);

getting this error:

Can not convert ObjectV to ArrayV

The response to your query is a JSON object, which contains an array (in the data field), but is not itself an object. That’s why you’re getting that error: the object is not an array.

The Fauna Value type has some useful accessors. You can see the implementation here: faunadb-jvm/Value.java at v5 · fauna/faunadb-jvm · GitHub

Given your query, and the sample response that you provided, if you wanted to list each titolo and autore field in the response, you could do something like this:

    Value value = client.query(
        Map(
            Paginate(
                Match(Index("all_titoli"))
            ),
            Lambda("X", Get(Var("X")))
        )
    ).get();

    // Access the array of documents in the response
    Collection<Value> allDocuments = value.at("data").asCollectionOf(Value.class).get();

    // Create an iterator to iterate over the documents
    Iterator<Value> iterator = allDocuments.iterator();

    // Iterate over the documents
    while (iterator.hasNext()) {
        // acquire the current document from the iterator
        Value current = iterator.next();

        // access each field from the current document
        String titolo = current.at("data", "titolo").to(String.class).get();
        String autore = current.at("data", "autore").to(String.class).get();

        // Print out the field values
        System.out.println("titolo= " + titolo);
        System.out.println("autore= " + autore);
    }

When I run this, after setting up a database with data to match your sample response, I get:

titolo= canzone1
autore= autore1
titolo= canzone2
autore= autore2