@Cacheable with Publisher does not work

[rburgst]

In Micronaut 1.0.2 the @Cacheable annotation does not work on a method that returns a Publisher.

Service Method:

@Singleton
open class HelloService {
    val logger = LoggerFactory.getLogger(this.javaClass)

    @Cacheable("num-cache")
    @SingleResult
    open fun calculateValue(num: Int): Publisher<String> {
        logger.info("Calculating value for {}", num)
        return Flowable.just("Hello $num")
    }
}

Cache config in application.yml

micronaut:
    application:
        name: cacheable-sample
    caches:
        num-cache:
            expire-after-write: 10m

Steps to Reproduce

1. run the app

   ./gradlew run

2. send an http request multiple times

   http :8080/hello

Expected Behaviour

the method HelloService.calculateValue(0) should only be called once, which should produce the following
output:

20:18:07.133 [nioEventLoopGroup-1-3] INFO  c.s.$HelloServiceDefinition$Intercepted - Calculating value for 0

Actual Behaviour

the method is called multiple times producing the output

20:17:53.374 [nioEventLoopGroup-1-2] INFO  c.s.$HelloServiceDefinition$Intercepted - Calculating value for 0
20:18:07.133 [nioEventLoopGroup-1-3] INFO  c.s.$HelloServiceDefinition$Intercepted - Calculating value for 0
20:18:17.442 [nioEventLoopGroup-1-3] DEBUG i.m.c.interceptor.CacheInterceptor - Value found in cache [num-cache] for invocation: Publisher calculateValue(int num)
20:18:20.828 [nioEventLoopGroup-1-4] INFO  c.s.$HelloServiceDefinition$Intercepted - Calculating value for 0
20:18:23.043 [nioEventLoopGroup-1-4] DEBUG i.m.c.interceptor.CacheInterceptor - Value found in cache [num-cache] for invocation: Publisher calculateValue(int num)

Environment Information

• Operating System: Mac OSX Mojave
• Micronaut Version: 1.0.3
• JDK Version: 1.8.0_181

Example Application

https://github.com/rburgst/cacheable-sample

[rburgst]

Please note that in my real app I am trying to cache calls to UserFetcher therefore, I cannot change the method signature:

open class UserFetcherService(private val userRepository: UserRepository) : UserFetcher {
    @Cacheable("user-cache")
    @SingleResult
    @Transactional
    open override fun findByUsername(username: String?): Publisher<UserState> {
...

[graemerocher]

As far as I can see this is behaving correctly. The method is invoked once to retrieve the publisher then the result of subscribing to the publisher is cached, not the publisher itself.

This behaviour can be seen in the test I committed da143f0

It doesn't really make sense to cache the publisher itself in the reactive case, so what Micronaut does is subscribe to the publisher and cache the result of the subscription as this is what is normally expensive. You can rewrite your code to return a callable which will get the behaviour you want:

ie

       Publisher<String> calculateValue(Integer num) {
            return Flowable.fromCallable({->
                println("Calculating value for $num")
                return "Hello $n: $num".toString()
            })
        }

[rburgst]

this does indeed work, however, I guess the documentation/code sample in http://guides.micronaut.io/micronaut-database-authentication-provider-groovy/guide/index.html#userFetcher should be adapted as it will steer people in a wrong direction