How to handle a multiple singles?

Question

I'm writing messenger server on grpc with rxjava2 stubs, and I stuck on combining my singles.

I'm have tried some sort of

  val user:Single<User> = getUser()
  val conversation:Single<Conversation> = getConversation(user.blockingGet())
  return conversation.map{
      someMethod(user.blockingGet(), conversation.it())
      it
  }

It looks so unbeauty then all of the examples, so is there a way to combine all of this singles to one line?

Answer 1

First a small comment, usually you don't want to use blockingGet. Instead you use other combinators to compose your solution and in the end you use subscribe to evaluate it.

I'm assuming you want to combine multiple calls that return a Single where the result of the next call depends on the previous.

The combinator you are looking for is flatMap.

val user: Single<User> = getUser()
val singleOfSomething: Single<Conversation> = user.flatMap { user-> 
    getConversation(user).flatMap {conversation -> 
        someMethod(user, conversation) 
    }
} 

here the return type would be Single of whatever someMethod returns.

You would use subscribe to get that value out when you need it.