How do you extract a value from a Mono type field?

Question

I am new to java reactive and am spinning my wheels on what I would think is a pretty easy thing to do.

My intent is to evaluate the result of a method call that returns a Mono type value and then determine a course of action based on that result. In the below example, if fieldAExists is true, I want to run the code that performs the update at the latter part of the addFieldA method.

How is a Boolean value extracted from a Mono type value? Is it possible to extract the value out from the Mono field? I tried working with subscribe() but could not get it to return a value to me evaluate.

Can the two reactive statements be combined to form one statement? Any direction you can offer is appreciated.

public Mono addFieldA(Email email, String fieldA) {

    Mono fieldAExists = checkFieldAExistence(email);

    // if fieldAExists is true, call the below.
    return reactiveMongoTemplate.updateMulti(query(where("customer.email.address").is(email.address())),
            new Update().set("customer.publicId", fieldA), Account.class, accountCollection).map(result -> {
        if (result.wasAcknowledged()) {
            return true;
        } else {
            throw new IllegalArgumentException(
                    "Error adding fieldA value to customer with email address " + email.address());
        }
    });
}

public Mono checkFieldAExistence(Email email) {

    return reactiveMongoTemplate
            .findOne(query(where("customer.email.address").is(email.address()).and("customer.fieldA").ne(null)),
                    Account.class, accountCollection)
            .map(found -> true).switchIfEmpty(Mono.just(false));
}

user_1554633 · Answer

You can combine them with flatMap like this:

public Mono addFieldA(Email email, String fieldA) {

    return checkFieldAExistence(email).flatMap(fieldAExists -> {
        if (fieldAExists) {
            return reactiveMongoTemplate.updateMulti(query(where("customer.email.address").is(email.address())),
                    new Update().set("customer.publicId", fieldA), Account.class, accountCollection).map(result -> {
                if (result.wasAcknowledged()) {
                    return true;
                } else {
                    throw new IllegalArgumentException(
                            "Error adding fieldA value to customer with email address " + email.address());
                }
            });
        } else {
            return Mono.just(false);
        }
    });
}

How do you extract a value from a Mono<Boolean> type field?

1 Answers