Package akka.cluster.sharding.typed.scaladsl

Interface EntityRef<M>

  • All Superinterfaces:
    RecipientRef<M>
    public interface EntityRef<M>
extends RecipientRef<M>
    A reference to an sharded Entity, which allows ActorRef-like usage.

    An EntityRef is NOT an ActorRef–by design–in order to be explicit about the fact that the life-cycle of a sharded Entity is very different than a plain Actors. Most notably, this is shown by features of Entities such as re-balancing (an active Entity to a different node) or passivation. Both of which are aimed to be completely transparent to users of such Entity. In other words, if this were to be a plain ActorRef, it would be possible to apply DeathWatch to it, which in turn would then trigger when the sharded Actor stopped, breaking the illusion that Entity refs are "always there". Please note that while not encouraged, it is possible to expose an Actor's self ActorRef and watch it in case such notification is desired. Not for user extension.

    • Method Detail

      • $bang

        void $bang​(M msg)
        Send a message to the entity referenced by this EntityRef using *at-most-once* messaging semantics.

        Example usage: 

        
 val target: EntityRef[String] = ...
 target ! "Hello"

      • $qmark

        <Res> scala.concurrent.Future<Res> $qmark​(scala.Function1<ActorRef<Res>,​M> message,
                                          Timeout timeout)
        Allows to "ask" the EntityRef for a reply. See AskPattern for a complete write-up of this pattern

        Note that if you are inside of an actor you should prefer akka.actor.typed.scaladsl.ActorContext.ask as that provides better safety.

        Example usage: 

        
 case class Request(msg: String, replyTo: ActorRef[Reply])
 case class Reply(msg: String)

 implicit val timeout = Timeout(3.seconds)
 val target: EntityRef[Request] = ...
 val f: Future[Reply] = target ? (replyTo => Request("hello", replyTo))

        Please note that an implicit Timeout must be available to use this pattern.

        Note: it is preferable to use the non-symbolic ask method as it easier allows for wildcards for the replyTo: ActorRef.

      • ask

        <Res> scala.concurrent.Future<Res> ask​(scala.Function1<ActorRef<Res>,​M> f,
                                       Timeout timeout)
        Allows to "ask" the EntityRef for a reply. See AskPattern for a complete write-up of this pattern

        Note that if you are inside of an actor you should prefer akka.actor.typed.scaladsl.ActorContext.ask as that provides better safety.

        Example usage: 

        
 case class Request(msg: String, replyTo: ActorRef[Reply])
 case class Reply(msg: String)

 implicit val timeout = Timeout(3.seconds)
 val target: EntityRef[Request] = ...
 val f: Future[Reply] = target.ask(Request("hello", _))

        Please note that an implicit Timeout must be available to use this pattern.

      • dataCenter

        scala.Option<java.lang.String> dataCenter()
        The specified datacenter of the incarnation of the particular entity referenced by this EntityRef, if a datacenter was specified.

      • entityId

        java.lang.String entityId()
        The identifier for the particular entity referenced by this EntityRef. 

        
 // given sharding, typeKey
 sharding.entityRefFor(typeKey, "someId").entityId == "someId"  // always true

      • tell

        void tell​(M msg)
        Send a message to the entity referenced by this EntityRef using *at-most-once* messaging semantics.

        Example usage: 

        
 val target: EntityRef[String] = ...
 target.tell("Hello")
        Specified by:
        tell in interface RecipientRef<M>

      • typeKey

        EntityTypeKey<M> typeKey()
        The EntityTypeKey associated with this EntityRef.