V1.3: Share Code

Actions as objects have a lot of advantages but they make code sharing less intuitive. This section shares a few techniques to make this possible.

Prepare

In our settings (apps/web/application.rb), there is a code block that allows us to share the code for all the actions of our application. When an action includes the Web::Action module, that block code is yielded within the context of that class. This is heavily inspired by Ruby Module and its included hook.

Imagine we want to check if the current request comes from an authenticated user.

We craft a module in apps/web/controllers/authentication.rb.

# apps/web/controllers/authentication.rb
module Web
  module Authentication
    def self.included(action)
      action.class_eval do
        before :authenticate!
        expose :current_user
      end
    end

    private

    def authenticate!
      halt 401 unless authenticated?
    end

    def authenticated?
      !!current_user
    end

    def current_user
      @current_user ||= UserRepository.new.find(session[:user_id])
    end
  end
end

Once included by an action, it will set a before callback that executes :authenticate! for each request. If not logged in, a 401 is returned, otherwise the flow can go ahead and hit #call. It also exposes current_user for all the views (see Exposures).

It will be really tedious to include this module for all the actions of our app. We can use controller.prepare for the scope.

# apps/web/application.rb
require_relative './controllers/authentication'

module Web
  class Application < Hanami::Application
    configure do
      controller.prepare do
        include Web::Authentication
      end
    end
  end
end

Code included via prepare is available for ALL the actions of an application.

Skipping A Callback

Let’s say we have included Authentication globally, but want to skip the execution of its callback for certain resources. A typical use case is to redirect unauthenticated requests to our sign in form.

The solution is really simple and elegant at the same time: override that method.

# apps/web/controllers/sessions/new.rb
module Web
  module Controllers
    module Sessions
      class New
        include Web::Action

        def call(params)
          # ...
        end

        private
        def authenticate!
          # no-op
        end
      end
    end
  end
end

The action will still try to invoke :authenticate!, because, technically speaking, callbacks execution can’t be skipped. But if we override that method with an empty implementation, it does nothing and our non-signedin users can reach the wanted resource.

Module Inclusion

Imagine we have a RESTful resource named books. There are several actions (show, edit, update and destroy) which need to find a specific book to perform their job.

What if we want to DRY the code of all these actions? Ruby comes to our rescue.

# apps/web/controllers/books/set_book.rb
module Web
  module Controllers
    module Books
      module SetBook
        def self.included(action)
          action.class_eval do
            before :set_book
          end
        end

        private

        def set_book
          @book = BookRepository.new.find(params[:id])
          halt 404 if @book.nil?
        end
      end
    end
  end
end

We have defined a module for our behavior to share. Let’s include it in all the actions that need it.

# apps/web/controllers/books/update.rb
require_relative './set_book'

module Web
  module Controllers
    module Books
      class Update
        include Web::Action
        include SetBook

        def call(params)
          # ...
        end
      end
    end
  end
end