Query That Returns Either a Result or null

Axon Framework
1

Hi, I’m struggling with a case, which I thought would be an easy thing.

What I want to achieve is a query handler that either returns an instance of the type to be returned or null, of there is no instance.

Regardless, of whatever I try, in case of non existing instances (which would let the query handler return null), I get exceptions saying that org.axonframework.serialization.UnknownSerializedType can’t be casted to the desired type.

What is the best practice for query handlers that might have to indicate that a certain queried does not exist?

Thanks

2

Have you tried the ResponseType Optional? This should do exactly what you need.

So the queryHandler method returns Optional (via Optional.ofNullable(t)) and you query via queryGateway.query(query, ResponseTypes.optionalInstanceOf(T.class))

3

Thanks Jan, yes I think I tried that too… but I’m not sure (I tried a lot of different things). So I’ll try your suggestion and let you know.

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