CustomDataFetcher

CustomDataFetcher.kt

package com.example.demographql.config

import com.expediagroup.graphql.execution.FunctionDataFetcher
import graphql.schema.DataFetchingEnvironment
import reactor.core.publisher.Flux
import reactor.core.publisher.Mono
import kotlin.reflect.KFunction

class CustomFunctionDataFetcher(target: Any?, fn: KFunction<*>) : FunctionDataFetcher(target, fn) {

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

    override fun get(environment: DataFetchingEnvironment): Any? {
        return convert(environment)
    }
}

CustomDataFetcherConfig.kt

package com.example.demographql.config

import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration
class CustomDataFetcherConfig {
    @Bean
    fun dataFetcherFactoryProvider() = CustomDataFetcherFactoryProvider()
}

CustomDataFetcherFactoryProvider.kt

package com.example.demographql.config

import com.expediagroup.graphql.execution.SimpleKotlinDataFetcherFactoryProvider
import graphql.schema.DataFetcherFactory
import kotlin.reflect.KFunction

class CustomDataFetcherFactoryProvider(
) : SimpleKotlinDataFetcherFactoryProvider() {

    override fun functionDataFetcherFactory(target: Any?, kFunction: KFunction<*>): DataFetcherFactory<Any?> = DataFetcherFactory {
        CustomFunctionDataFetcher(
                target = target,
                fn = kFunction)
    }

}