Missing an OptionalResponseType for query that return Optional<R>

Hi all,

I’ve just tested the last version of Axon framework (3.2) and I ran into an issues with queries that return an Optional:

 queryGateway.query(query, Optional.class)

Axon still complains that it can’t find a handler for my optional, despite I have a @QueryHandler for my query.

It would be great to have an OptionalResponseType like MultipleInstancesResponseType that can handle Optionals.

I’ve try something like this:

public class OptionalResponseType<R> extends AbstractResponseType<Optional<R>> {
private OptionalResponseType(Class<?> expectedResponseType) {
    super(expectedResponseType);
}

@Override
public boolean matches(Type responseType) {
    return isParameterizedType(responseType) &&
            isParameterizedTypeOfExpectedType(responseType) &&
            isOptional(responseType);
}

@SuppressWarnings("unchecked")
private boolean isOptional(Type responseType) {
    return ((Class)((ParameterizedType) responseType).getRawType()).isAssignableFrom(Optional.class);
}

@Override
@SuppressWarnings("unchecked")
public Optional<R> convert(Object response) {        
    if (response instanceof Optional) {
        return super.convert(response);
    } else {
        return Optional.ofNullable((R) response);
    }
}

public static <R> ResponseType<Optional<R>> optionalInstancesOf(Class<R> type) {
    return new OptionalResponseType<>(type);
}

}

It seems to work but it would be cool to have it in org.axonframework.queryhandling.responsetypes.ResponseTypes

Regards, Sylvain

[smcvb]

Thanks for sharing that @thomaslhostis, but there currently is an OptionalResponseType implementation in Axon Framework you can use for this scenario. Here is the implementation, which has been introduced in Axon 4.2.

Hence upgrading to a more recent version (currently this is 4.4.3) will allow you to use it.

[thomaslhostis]

@FabianTe This is how @Sylvain-maillard implemented it using version 3.4 of Axon : https://github.com/voyages-sncf-technologies/hesperides/blob/master/commons/src/main/java/org/hesperides/commons/axon/AxonResponseType.java

And how we use it: https://github.com/voyages-sncf-technologies/hesperides/blob/267f30da8c6bc2b42e309fcbce3293c99366d1cb/commons/src/main/java/org/hesperides/commons/axon/AxonQueries.java#L49