A complete rails admin custom action, the file of this gist are the paths were you should put your files

app assets javascripts rails_admin actions create_aliada_working_hours.js

alert('omg hi!')

app assets stylesheets rails_admin custom theming.css.sass

.create_aliada_working_hours
  background: grey

app models admin_ability.rb

# If you use can can for your admin you'll have to add in your admin ability
can :create_aliada_working_hours

app views rails_admin main create_aliada_working_hours.html.haml

.create_aliada_working_hours
  Lets do some cool stuff!

= javascript_include_tag 'rails_admin/actions/create_aliada_working_hours'

config initializers rails_admin.rb

# Register actions at the top of the file
RailsAdmin::Config::Actions.register(:create_aliada_working_hours, RailsAdmin::Config::Actions::CreateAliadaWorkingHours)

# Inside the actions block
  config.actions do
    create_aliada_working_hours do
      visible do
        bindings[:abstract_model].model.to_s == 'Aliada'
      end
    end
  end

config locales rails_admin_es.yml

en:
  admin:
    actions:
      create_aliada_working_hours:
        title: Create aliada working hours
        menu: Create aliada working hours
        breadcrumb: Create aliada working hours

lib rails_admin config actions create_aliada_working_hours.rb

# -*- encoding : utf-8 -*-
require 'rails_admin/config/actions'
require 'rails_admin/config/actions/base'

module RailsAdmin
  module Config
    module Actions
      class CreateAliadaWorkingHours < RailsAdmin::Config::Actions::Base
        RailsAdmin::Config::Actions.register(self)

        register_instance_option :member? do
          true
        end

        register_instance_option :http_methods do
          [:get, :post]
        end

        register_instance_option :link_icon do
          # Escoger uno bonito de http://getbootstrap.com/2.3.2/base-css.html#icons
          'icon-time'
        end

        # Might cause random bugs if enabled
        register_instance_option :pjax? do
          false
        end

        register_instance_option :controller do
          Proc.new do
            next render :action => @action.template_name if !request.post?

            aliada_id = params[:id]

            if AliadaWorkingHour.update_from_admin(aliada_id: aliada_id)
              redirect_to back_or_index
            else
              render json: {status: :success, url: rails_admin.create_aliada_working_hours_path}
            end
          end
        end
      end
    end
  end
end