Inter service communication - injection of service B in to serviceAImpl fails compiling (with out message broker trying remote call) - lagom

Question

I am a beginner of Lagom and using it with Scala. It is an awesome experience for me to create a microservice using it till now.
As I referred the following
https://www.lagomframework.com/documentation/1.4.x/scala/ServiceClients.html#Binding-a-service-client
and I am trying out for calling inter service with out message broker via remote calls. Which means I wanted to inject ServiceB in to serviceAImpl and do a invoke call on the client.This is for one of the scenario where I dont want the call to be via Event or message broker and should be a direct service to service call.
In Lagom scala I have ServiceA and ServiceB. I have created a ServiceB client in the ServiceAApplication and trying to inject the serviceB in the ServiceAImpl. I get an error during compilation saying the following,
Cannot find a value of type : [com.example.ServiceB]
override lazy val lagomServer = serverForServiceA
in the abstract class ServiceAApplication
snippet of the ApplicationLoader class where I get this error only when I inject the ServiceB in to the ServiceAImpl constructor.
Snippet of ServiceAApplicationLoader.scala:
trait ServiceAComponents extends LagomServerComponents
with SlickPersistenceComponents
with LagomConfigComponent
with HikariCPComponents
with LagomKafkaComponents
{
implicit def executionContext: ExecutionContext
def environment: Environment
implicit def materializer: Materializer
override lazy val lagomServer = serverFor[ServiceA](wire[ServiceAImpl])
lazy val serviceARepository = wire[ServiceARepository]
lazy val jsonSerializerRegistry = ServiceASerializerRegistry
persistentEntityRegistry.register(wire[ServiceAEntity])
readSide.register(wire[ServiceAEventProcessor])
}
abstract class ServiceAApplication(context: LagomApplicationContext) extends LagomApplication(context)
with ServiceAComponents
with AhcWSComponents
with SlickPersistenceComponents
with LagomServiceClientComponents
with LagomConfigComponent
{
lazy val serviceB = serviceClient.implement[ServiceB]
}
`class ServiceAApplicationLoader extends LagomApplicationLoader {
override def load(context: LagomApplicationContext) =
new ServiceAApplication(context) with LagomServiceLocatorComponents
override def loadDevMode(context: LagomApplicationContext) =
new ServiceAApplication(context) with LagomDevModeComponents
override def describeService = Some(readDescriptor[ServiceA])
}
`
Snippet of ServiceAImpl.scala:
class ServiceAImpl (registry: PersistentEntityRegistry, serviceARepository:ServiceARepository ,serviceB: ServiceB )
(implicit ec: ExecutionContext) extends ServiceA {
/// Here in one of the method calling serviceB which is injected in constructor.
When I compile I get the error as following :
Cannot find a value of type : [com.example.ServiceB]
override lazy val lagomServer = serverForServiceA
Note: When I do the application loader in the following way, I dont get the error, But as you will seee below, I dont define a component and hence losing the testability:
I dont have a trait for th ServiceAComponent like above, instead have defined as below.
abstract class ServiceAApplication(context: LagomApplicationContext) extends LagomApplication(context)
with ServiceAComponents
with AhcWSComponents
with SlickPersistenceComponents
with LagomServiceClientComponents
with LagomConfigComponent
{
override lazy val lagomServer = serverFor[ServiceA](wire[ServiceAImpl])
lazy val serviceARepository = wire[ServiceARepository]
lazy val jsonSerializerRegistry = ServiceASerializerRegistry
persistentEntityRegistry.register(wire[ServiceAEntity])
readSide.register(wire[ServiceAEventProcessor])
lazy val serviceB = serviceClient.implement[ServiceB]
}
class ServiceAApplicationLoader extends LagomApplicationLoader {
override def load(context: LagomApplicationContext) =
new ServiceAApplication(context) with LagomServiceLocatorComponents
override def loadDevMode(context: LagomApplicationContext) =
new ServiceAApplication(context) with LagomDevModeComponents
override def describeService = Some(readDescriptor[ServiceA])
}
This Application Loader works fine with runAll, but if I have to run with unit test as there is no component trait found, not able to run along with the ServiceB.
snippet of unittest:
class ServiceAImplIntegrationTest extends AsyncWordSpec with Matchers with BeforeAndAfterAll {
private val server = ServiceTest.startServer(ServiceTest.defaultSetup.withCassandra(true)) { ctx=>
new ServiceAApplication(ctx) with LocalServiceLocator{
override def additionalConfiguration: AdditionalConfiguration =
super.additionalConfiguration ++ ConfigFactory.parseString(
"cassandra-query-journal.eventual-consistency-delay = 0"
)
}
}
Note: If you see the test case, it does not follow the way it is done in the sample ItemIntegrationTest, instead of starting the server with Component, I have started with just ServiceAApplication and hence the test fail saying service B is not running. How to deal with this.
Questions:
1. Is injecting a serviceB in to ServiceAImpl the right way and call it using invoke method ? (with out having a subscriber)
2. How to test this as integration of serviceA and serviceB ?

Answer 1

I have got answer in the following link
https://discuss.lightbend.com/t/inter-service-communication-with-out-message-broker-unable-to-inject-if-creating-component-extending-lagomservercomponent/3257
I changed the component defnition as mention in above link and that solved the issue.