feature: allow for returning Mono/Flux within dataFetchers/mutations.

[ruseinov]

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Describe the Feature Request

Currently when one returns a Mono/Flux within, for example, a DataFetcher - that results in a null.
There are more details here: Netflix/dgs-examples-webflux#5 and a workaround that involves converting Mono/Flux to a CompletableFuture.

One of the use-cases for this is DGS + Webflux + ReactiveMongoTemplate integration. At the moment that requires extra effort/boilerplate and I am guessing a slight overhead, because the CompletableFuture returned by the Datafetchers is then converted back to Mono.
It also makes using reactive Mongo with DGS + Webflux a bit confusing, because when using Spring MVC you can use Mongo/Flux as return types for your endpoints and in DGS it results in an error.

Describe Preferred Solution

Allow for returning a Mono/Flux within Mutations/Datafetchers/Subscriptions and automatically convert those to Entities/Lists of entities.

Describe Alternatives

Could be seen in Netflix/dgs-examples-webflux#5 , basically converting reactor stuff to CompletableFutures.

[driverpt]

+1

[paulbakker]

This obviously makes sense to support. The one problem is that graphql-java doesn't support Flux/Mono, so internally everything still has to be CompletableFuture.

I've added some code that basically does the conversion automatically. I think that would work well, but please test it out.

#389

[paulbakker]

This was released in: https://github.com/Netflix/dgs-framework/releases/tag/v4.2.0

[ruseinov]

Thanks a lot!