Actors

When you create or update a Work in curation_concerns, there are a number of processing steps involved, and a specific format for doing so. This format is a stack (last in, first out). Each frame does one thing, and the whole stack must be executed in the order it's written in.

Each processing step, or frame, is broken out into a class called an Actor. They do common tasks like add a Work to a collection, add a Work to another Work, assign a representative file to Work, and apply order to a Work.

Code that wishes to use the whole stack of actors should call CurationConcerns::CurationConcern.actor. That method returns an instance of CurationConcerns::ActorStack, which is the full list of operations to perform to create or update a Work.

This ActorStack is instantiated by an ActorFactory. The default factory is: CurationConcerns::ActorFactory, but you can change it by setting CurationConcerns::CurationConcern.actor_factory=. For example, Sufia wants to use its own factory, so it sets CurationConcerns::CurationConcern.actor_factory = Sufia::ActorFactory

Sufia's ActorFactory uses a different set of operations than the CurationConcerns version, but other than that it's the same. Sufia::ActorFactory inherits from the version in CurationConcerns, and overrides the stack_actors class method like so:

module Sufia
  class ActorFactory < CurationConcerns::ActorFactory
    def self.stack_actors(curation_concern)
      [CreateWithFilesActor,
       CurationConcerns::AddToCollectionActor,
       CurationConcerns::AssignRepresentativeActor,
       CurationConcerns::AttachFilesActor,
       CurationConcerns::ApplyOrderActor,
       CurationConcerns::InterpretVisibilityActor,
       model_actor(curation_concern),
       CurationConcerns::AssignIdentifierActor]
    end
  end
end

Each of the actors in this chain should inherit from CurationConcerns::AbstractFactory, and can override update() or create() as required. In these methods they must call next_actor.update(attributes) or next_actor.create(attributes) respectively. Here's an example:

module CurationConcerns
  class ApplyOrderActor < AbstractActor
    def update(attributes)
      ordered_member_ids = attributes.delete(:ordered_member_ids)
      apply_order(ordered_member_ids) && next_actor.update(attributes)
    end

    private

      def apply_order(new_order)
        ...
      end
  end
end