What is the correct way to resolve an actor

Question

I have 1000 orders and I want to create an actor for each unique orderid. What would be the best way to safely create these actors while guaranteeing that I only have one per unique orderid?

I have tried to first use ActorSelection, then if I can't find an actor with that id, I use ActorOf to create a new one, but when starting batches of these I will get a lot of ActorNotFoundException and when I then try to use ActorOf it fails with InvalidActorNameException.

Example:

try
{
    actorRef = await actorSelection.ResolveOne(TimeSpan.FromMilliseconds(3000));
}
catch (ActorNotFoundException)
{
    actorRef = Actor.EwmsActorSystem.ActorOf<T>(actorId);
}

Answer 1

You should use the Entity Per Child Pattern , ie have an actor that spawns child actors per entity ID. You can view an example in the World Crawler sample.

In a nutshell, it should look something like this:

var child = Context.Child(entityId.ToString());

if (child == ActorRefs.Nobody)
    child = Context.ActorOf(...); // spawn child actor here

child.Tell(message);

It is also good practice to set a ReceiveTimeout on the child actors, to kill them off when they have been idle for a period of time.