Using Reform with a Workflow object to allow the controller to be simpler.

artist_controller.rb

class ArtistsController < ApplicationController

  def create
    @form = create_new_form
    workflow = Workflows::ArtistWorkflow.new(@form, params[:artist])

    workflow.process do |obj|
      return respond_with obj
    end
    render :new
  end

  def update
    @form = create_edit_form
    workflow = Workflows::ArtistWorkflow.new(@form, params[:artist])

    workflow.process do |obj|
      return respond_with obj
    end
    render :edit
  end

  private
  def create_new_form
    ArtistForm.new(artist: Artist.new, song: StudentProfile.new)
  end

  def create_edit_form
    artist = Artist.find(params[:id])
    ArtistForm.new(artist: artist, song: artist.song)
  end

end

artist_workflow.rb

module Workflows
  class ArtistWorkflow
    attr_reader :form, :params

    def initialize(form, params)
      @form = form
      @params = params
    end

    def process
      if form.validate(params)
        form.save do |data, map|
          if form.student.new_record?
            new_artist = Services::CreateArtistWithSong(map[:student], map[:song]).call
            NotifyArtistCreation(new_artist).call
          else
            new_artist = Service::ManageArtistWithSong.new(map[:student], map[:profile]).update(form.artist.id, form.song.id)
          end

          yield new_artist if block_given?
        end
      end
    end

  end
end