I’m experimenting with graphq-kotlin and I wonder if it possible to get a response which combines errors and data. Currently when any of my data fetcher fails, the whole response fails and there is no

data

section in the response, only

errors

. Is it possible to get a response which would give me values for fetcher who did not fail and errors for the fetchers which fail? Something like this:

{
    "data": {
        "item": {
            "foo": "foo"
        },
    }
    "errors": [
        {
            "message": "Exception while fetching data (error) : I wonder what happends",
            "locations": [
                {
                    "line": 5,
                    "column": 3
                }
            ],
            "path": [
                "bar"
            ],
            "extensions": {}
        }
    ]
}

Yes you can, you have to return a

DataFetcherResult<*>

as the return type https://expediagroup.github.io/graphql-kotlin/docs/schema-generator/execution/exceptions#returning-data-and-errors

I see - so it is not possible to use the framework in a way so I can just throw an exception in my method and make sure this exception gets rolled in into errors?

Well using DataFetcherResult is using the framework. We have code to handle this return type and extract the info. Throwing an exception breaks the execution so the expectation in that's case is it is an error alone. If you have some other code that may throw an exception you should handle it then return the DataFetcherResult based on your logic

Ok - specifically for my case - I’m using Spring Webflux and Reactor and I wanted to design in a way it returns a valid value for a value coming from Mono/Flux stream and it returns the error in the case the stream fails with error. At this point I’m doing the mapping by extending

SpringDataFetcher

and overriding

get

method to return a future:

override fun get(environment: DataFetchingEnvironment): Any? = when (val result = super.get(environment)) {
        is Mono<*> -> result.toFuture()
        else -> result
    }
}

I’m wondering - would it be possible to extend this to do the conversion to DataFetcherResult right here?

You can use the

willResolveMonad

hook to unwrap any types that you may have. But in the code it self you would still need to return either a

CompletableFuture<DataFetcherResult<T>>

or

DataFetcherResult<T>

https://expediagroup.github.io/graphql-kotlin/docs/schema-generator/execution/async-models#rxjavareactor

Thanks, will try it out later today and let you know.