Customizing Actors

When you create, update, or destroy a Work in Hyrax, 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 Hyrax actors should call Hyrax::CurationConcern.actor. That method (by default) returns an instance of Hyrax::DefaultMiddlewareStack, which is the full list of operations to perform in order to create, update, or destroy a Work.

This stack is instantiated by an actor factory. The default factory, as stated above, is Hyrax::DefaultMiddlewareStack; if you want complete control over the stack, you can swap in your own customized factory by setting Hyrax::CurationConcern.actor_factory= in the Hyrax initializer (config/initializers/hyrax.rb).

You can also make targeted changes to Hyrax's actor stack like so (within a config/initializers/hyrax.rb):

# Adding a new middleware
Hyrax::CurationConcern.actor_factory.use MyCustomActor

# Inserting a new middleware at a specific position
Hyrax::CurationConcern.actor_factory.insert_after Hyrax::Actors::CreateWithRemoteFilesActor, MyCustomActor

# Removing a middleware
Hyrax::CurationConcern.actor_factory.delete Hyrax::Actors::CreateWithRemoteFilesActor

# Replace one middleware with another
Hyrax::CurationConcern.actor_factory.swap Hyrax::Actors::CreateWithRemoteFilesActor, MyCustomActor

Each of the actors in this chain should inherit from Hyrax::AbstractActor, and can override #update, #create, and/or #destroy as necessary. In these methods, they must call next_actor.update(env), next_actor.create(env), and/or next_actor.destroy(env) respectively. Here's an example:

module MyApp
  class ReverseOrderActor < AbstractActor
    def update(env)
      ids = env.attributes.delete(:domain_resource_ids)
      reverse_order(ids) && next_actor.update(env)
    end

    private

      def reverse_order(ids)
        ids.reverse
      end
  end
end