Can't use Spring Security annotation when injecting DataLoader and returning a CompletableFuture

[koenpunt]

I'm having trouble combining DataLoaders with Spring Security;

My scenario;

typealias MerchantDataLoader = DataLoader<UUID, Merchant?>

// MerchantDataLoader
registry.forTypePair(UUID::class.java, Merchant::class.java).registerMappedBatchLoader { merchantIds, _ ->
    Mono.just(merchantService.getMerchants(merchantIds).associateBy { it.id })
}

// ...

@SchemaMapping
@PreAuthorize("@permissionEvaluator.hasPermission(authentication, #merchant.id, 'Merchant', 'read')")
fun dashboardForDate(
    merchant: Merchant,
    @Argument date: LocalDate?,
    merchantLoader: MerchantDataLoader
): CompletableFuture<Dashboard> = merchantLoader.load(merchant.id).thenApply {
    if (it == null) throw EntityNotFoundException()
    Dashboard(date, it)
}

For GraphQL Java being able to dispatch the dataloader the method has to return the CompletableFuture, but for the @PreAuthorize annotation it "must return an instance of org.reactivestreams.Publisher (i.e. Mono / Flux) or the function must be a Kotlin coroutine function".

I've also tried making it a suspend fun, while still returning the CompletableFuture, but then I get an error like does not match the type of the source Object 'class java.util.concurrent.CompletableFuture', which makes sense because my controller is not expecting the CompletableFuture.

Is my assumption correct, or is there a way around this that I don't know about?

[koenpunt]

Interestingly enough converting to a mono seems to work;

@SchemaMapping
@PreAuthorize("@permissionEvaluator.hasPermission(authentication, #merchant.id, 'Merchant', 'read')")
fun dashboardForDate(
    merchant: Merchant,
    @Argument date: LocalDate?,
    merchantLoader: MerchantDataLoader
): Mono<Dashboard> = merchantLoader.load(merchant.id).thenApply {
    if (it == null) throw EntityNotFoundException()
    Dashboard(date, it)
}.toMono()

Although I'm not sure if this is coincidental, or that this is supposed to work.

[rstoyanchev]

The method needs to return a reactive type for reactive context to propagate. So this is expected, but you're bringing up a good point that our examples with injecting a DataLoader and using it as is should at least be improved. Maybe we could even consider injecting an alternative ReactiveDataLoader type that returns Mono instead of CompletableFuture.

[koenpunt]

Maybe we could even consider injecting an alternative ReactiveDataLoader type that returns Mono instead of CompletableFuture.

So returning a mono is supposed to work for dataloaders? In comparison; awaiting the CompletableFuture in a suspend fun causes the application to lock-up.

And a ReactiveDataLoader sounds like a good idea!

[rstoyanchev]

So returning a mono is supposed to work for dataloaders?

Yes that should work. Mono and Flux are supported as return values for any DataFetcher with context propagation, through ContextDataFetcherDecorator.

[koenpunt]

Alright, good to know it's spring graphql specific.
I suppose this could be extended to support coroutines too?

[rstoyanchev]

Probably so, but need to investigate.