ActiveAdmin.rb

ActiveAdmin.setup do |config|

  # == Site Title
  #
  # Set the title that is displayed on the main layout
  # for each of the active admin pages.
  #
  config.site_title = "Balance Cafe"

  # Set the link url for the title. For example, to take
  # users to your main site. Defaults to no link.
  #
  # config.site_title_link = "/"

  # Set an optional image to be displayed for the header
  # instead of a string (overrides :site_title)
  #
  # Note: Aim for an image that's 21px high so it fits in the header.
  #
  # config.site_title_image = "logo.png"

  # == Default Namespace
  #
  # Set the default namespace each administration resource
  # will be added to.
  #
  # eg:
  #   config.default_namespace = :hello_world
  #
  # This will create resources in the HelloWorld module and
  # will namespace routes to /hello_world/*
  #
  # To set no namespace by default, use:
  #   config.default_namespace = false
  #
  # Default:
  # config.default_namespace = :admin
  #
  # You can customize the settings for each namespace by using
  # a namespace block. For example, to change the site title
  # within a namespace:
  #
  #   config.namespace :admin do |admin|
  #     admin.site_title = "Custom Admin Title"
  #   end
  #
  # This will ONLY change the title for the admin section. Other
  # namespaces will continue to use the main "site_title" configuration.

  # == User Authentication
  #
  # Active Admin will automatically call an authentication
  # method in a before filter of all controller actions to
  # ensure that there is a currently logged in admin user.
  #
  # This setting changes the method which Active Admin calls
  # within the application controller.
  config.authentication_method = :authenticate_admin_user!

  # == User Authorization
  #
  # Active Admin will automatically call an authorization
  # method in a before filter of all controller actions to
  # ensure that there is a user with proper rights. You can use
  # CanCanAdapter or make your own. Please refer to documentation.
  # config.authorization_adapter = ActiveAdmin::CanCanAdapter

  # You can customize your CanCan Ability class name here.
  # config.cancan_ability_class = "Ability"

  # You can specify a method to be called on unauthorized access.
  # This is necessary in order to prevent a redirect loop which happens
  # because, by default, user gets redirected to Dashboard. If user
  # doesn't have access to Dashboard, he'll end up in a redirect loop.
  # Method provided here should be defined in application_controller.rb.
  # config.on_unauthorized_access = :access_denied

  # == Current User
  #
  # Active Admin will associate actions with the current
  # user performing them.
  #
  # This setting changes the method which Active Admin calls
  # (within the application controller) to return the currently logged in user.
  config.current_user_method = :current_admin_user


  # == Logging Out
  #
  # Active Admin displays a logout link on each screen. These
  # settings configure the location and method used for the link.
  #
  # This setting changes the path where the link points to. If it's
  # a string, the strings is used as the path. If it's a Symbol, we
  # will call the method to return the path.
  #
  # Default:
  config.logout_link_path = :destroy_admin_user_session_path

  # This setting changes the http method used when rendering the
  # link. For example :get, :delete, :put, etc..
  #
  # Default:
  # config.logout_link_method = :get


  # == Root
  #
  # Set the action to call for the root path. You can set different
  # roots for each namespace.
  #
  # Default:
  # config.root_to = 'dashboard#index'


  # == Admin Comments
  #
  # This allows your users to comment on any resource registered with Active Admin.
  #
  # You can completely disable comments:
  # config.allow_comments = false
  #
  # You can disable the menu item for the comments index page:
  # config.show_comments_in_menu = false
  #
  # You can change the name under which comments are registered:
  # config.comments_registration_name = 'AdminComment'


  # == Batch Actions
  #
  # Enable and disable Batch Actions
  #
  config.batch_actions = true


  # == Controller Filters
  #
  # You can add before, after and around filters to all of your
  # Active Admin resources and pages from here.
  #
  # config.before_filter :do_something_awesome


  # == Setting a Favicon
  #
  # config.favicon = '/assets/favicon.ico'


  # == Removing Breadcrumbs
  #
  # Breadcrumbs are enabled by default. You can customize them for individual
  # resources or you can disable them globally from here.
  #
  # config.breadcrumb = false


  # == Register Stylesheets & Javascripts
  #
  # We recommend using the built in Active Admin layout and loading
  # up your own stylesheets / javascripts to customize the look
  # and feel.
  #
  # To load a stylesheet:
  #   config.register_stylesheet 'my_stylesheet.css'
  #
  # You can provide an options hash for more control, which is passed along to stylesheet_link_tag():
  #   config.register_stylesheet 'my_print_stylesheet.css', :media => :print
  #
  # To load a javascript file:
  #   config.register_javascript 'my_javascript.js'


  # == CSV options
  #
  # Set the CSV builder separator
  # config.csv_options = { :col_sep => ';' }
  #
  # Force the use of quotes
  # config.csv_options = { :force_quotes => true }


  # == Menu System
  #
  # You can add a navigation menu to be used in your application, or configure a provided menu
  #
  # To change the default utility navigation to show a link to your website & a logout btn
  #
  #   config.namespace :admin do |admin|
  #     admin.build_menu :utility_navigation do |menu|
  #       menu.add label: "My Great Website", url: "http://www.mygreatwebsite.com", html_options: { target: :blank }
  #       admin.add_logout_button_to_menu menu
  #     end
  #   end
  #
  # If you wanted to add a static menu item to the default menu provided:
  #
  #   config.namespace :admin do |admin|
  #     admin.build_menu :default do |menu|
  #       menu.add label: "My Great Website", url: "http://www.mygreatwebsite.com", html_options: { target: :blank }
  #     end
  #   end


  # == Download Links
  #
  # You can disable download links on resource listing pages,
  # or customize the formats shown per namespace/globally
  #
  # To disable/customize for the :admin namespace:
  #
  #   config.namespace :admin do |admin|
  #
  #     # Disable the links entirely
  #     admin.download_links = false
  #
  #     # Only show XML & PDF options
  #     admin.download_links = [:xml, :pdf]
  #
  #     # Enable/disable the links based on block
  #     #   (for example, with cancan)
  #     admin.download_links = proc { can?(:view_download_links) }
  #
  #   end


  # == Pagination
  #
  # Pagination is enabled by default for all resources.
  # You can control the default per page count for all resources here.
  #
  # config.default_per_page = 30


  # == Filters
  #
  # By default the index screen includes a “Filters” sidebar on the right
  # hand side with a filter for each attribute of the registered model.
  # You can enable or disable them for all resources here.
  #
  # config.filters = true
end

module ActiveAdmin::ViewHelpers
  include ApplicationHelper
  def show_image(p)
    p.object.image.nil? ? p.template.content_tag(:span, "No Upload Image Yet") : p.template.image_tag(p.object.image.url(:small))
  end
end

module ActiveAdmin
  module Views
    class Footer < Component

      def build
        super :id => "footer"
        super :style => "text-align: right;"
        div do
          small "Cool footer #{Date.today.year}"
        end
      end

    end
  end
end

product.rb

class Product < ActiveRecord::Base
  belongs_to :product_group
  has_many :photos, :dependent => :destroy
  accepts_nested_attributes_for :photos, allow_destroy: true

  validates_presence_of :product_group_id, :price, :name, :description

  def upload_images(params, image)
      photos.create(title: params['name'], image: image)
  end
end

products.rb

ActiveAdmin.register Product do

  form :html => { :multipart => true } do |f|
    f.inputs do
      f.input :product_group_id, :as => :radio, :collection => ProductGroup.all.map {|u| [u.name, u.id]}, :include_blank => false
      [:name, :description, :price,  :start_at, :end_at].each do |col|
        f.input col
      end
    end
     f.has_many :photos, heading: false, allow_destroy: true do |p|
        p.input :image, :as => :file, :label => "Image",:hint => show_image(p)
        p.input :_destroy, :as=>:boolean, :required => false, :label => 'Remove image'
     end
    f.actions
  end

  permit_params [:product_group_id,:name, :description, :price,  :start_at, :end_at, :photos_attributes=> [:id, :image, :_destroy]]

end