Frill

Simple decoration of objects for presentation. Out of the box integration with Rails.

Throw this in your Gemfile:

gem "frill"

Decorate your objects for presentation.

$ rails g frill FooFrill

Frills are just modules that decorate your objects with extra functionality. The frill? method on the module tells Frill when to decorate an object with a module:

module FooFrill
  def self.frill? object, context
    object.respond_to?(:foo)
  end

  def foo
    h.content_tag :b, "#{super} bar"
  end
end

The h method gives you access to all of the view helpers you would normally expect to use inside a view or a helper. It's aliased to helpers, so feel free to use either.

Opt objects in your controllers into frill with the frill method:

class FooController < ApplicationController
  def foo
    @foo = frill Foo.find(params[:id])
  end
end

Then just use the foo method on your Foo objects to get their decorated functionality:

Awesome foo page!

<%=@foo.foo%>

Instead of manually opting objects into decoration via the frill method, you can have all of your controller instance variables automatically decorated via the auto_frill macro:

class ApplicationController < ActionController::Base
  auto_frill
end

Now you don't need to use the frill method to decorate objects. They'll be automatically decorated before being passed off to your view.

class FooController < ApplicationController
  def foo
    @foo = Foo.find params[:id]
  end
end

The frill helper will decorate both single objects and collections of objects. You can use it both within your controller and within your views.

For example, inside a controller:

class FoosController < ApplicationController
  def index
    @foos = frill Foo.all
  end

  def show
    @foo = frill Foo.find(params[:id])
  end
end

Or, in a view:

<%= render frill(@foo.comments) %>

You can tell frill to consider only a subset of frills for decoration with the with option:

<%= render frill(@posts, with: [TextPostFrill, PicturePostFrill, VideoPostFrill])

If you want to specify the order in which frills are applied, you can use before and after in your frill modules:

module FooFrill
  before BarFrill
end

module BazFrill
  after BarFrill
end

module BarFrill
end

With this setup, frill will attempt to apply the modules in the following order: FooFrill, BarFrill, BazFrill.

Your product manager writes the following story for you:

Feature: Consistent Timestamp Presentation
  As a user
  I want "created at" timestamps presented in a uniform, localized way on the site
  So that I can easily discover the age of content on the site

  Scenario: Presenting timestamps
    When I navigate to a page that displays a created_at timestamp
    Then I should see that timestamp marked up as bold and formatted for the client's locale as follows: Month DD, YYYY HH:MM 

You see this and roll your eyes. You're thinking about all of the places that you show created_at timestamps on the site. Reluctantly, you roll up your sleeves and start by writing the following helper and partial:

module ApplicationHelper
  def format_timestamp(t)
    render partial: "shared/timestamp", locals: { time: l(t, format: :long) }
  end
end

<b><%=time%></b>

You then begin the tedious task of tracking down all of the places you render timestamps on the site and wrapping them with format_timestamp helper calls:

...
Written on <%=format_timestamp @article.created_at %>

You hate this approach.

1. It's tedious
2. It's procedural
3. Developers have to remember to manually wrap timestamps with your format_timestamp helper.

After you deliver the story, your product owner says "Great! But what about the format of timestamps in the JSON api? Here's another story."

Feature: Consistent Timestamp Presentation in the API
  As an API consumer
  I want "created at" timestamps presented in the API in uniform way
  So that I can easily discover the age of data I consume

  Scenario: Presenting timestamps
    When I retrieve content with a "created_at" timestamp via the JSON API
    Then I should see that timestamp formatted for the client's locale as follows: Month DD, YYYY HH:MM 

You attempt to salvage the helper, updating it with concerns for the JSON format:

module ApplicationHelper
  def format_timestamp(t)
    time = l t, format: :long 

    if request.format.html?
      render partial: "shared/timestamp", locals: { time: time }
    elsif request.format.json?
      time
    end
  end
end

And now you begin the tedious task of updating all of the JSON views with the helper:

json.created_at format_timestamp(@article.created_at)

At this point, you're banging your head against a table.

Let's refactor this using the decorator pattern. First, revert all of your changes. Next, add the frill gem to your Gemfile, run bundle, then generate a frill: rails g frill TimestampFrill:

module TimestampFrill
  include Frill

  def self.frill? object, context
    object.respond_to?(:created_at)
  end

  def created_at
    helpers.l super, format: :long
  end
end

The frill? method tells Frill when to extend an object with this module. Then we redefine the created_at method, calling super and then formatting the date with the rails localization helper l. The helpers method is made available to frill'ed objects; it contains the same view context that you have access to inside of views and inside of helper methods. You can use the h method as well - it's simply an alias for helpers.

Simple enough.

Next, generate another frill for presenting timestamps via HTML (rails g frill HtmlTimestampFrill):

module HtmlTimestampFrill
  include Frill
  after TimestampFrill

  def self.frill? object, context
    object.respond_to?(:created_at) && context.request.format.html?
  end

  def created_at
     h.render partial: "shared/timestamp", locals: { time: super }
  end
end

<b><%=time%></b>

There's three important things to note:

1. This frill comes after TimestampFrill. That tells Frill that it should only attempt to extend an object with this module after attempting to extend it with TimestampFrill.
2. The frill? method only returns true if it's an HTML request, meaning this frill won't be extended onto objects for your JSON api.
3. The h method gives you access to all of the normal view helper methods you expect to you use inside your views. You can also use helpers.

Lastly, opt objects into frilling inside your controllers by using the frill method:

class ArticlesController < ApplicationController
  respond_to :json, :html

  def show
    @article = frill Article.find(params[:id])
    respond_with @article
  end
end

And that's it. You don't have to update any of your views. Why? When you call the frill method inside your controller and pass it an object (or a collection of objects), frill will attempt to extend the object with any applicable frills (i.e., frills that return true for the frill? method when passed the object and the request context).

That way, you can simply render your created_at attributes without any helpers, and they will automatically present themselves appropriately for their context (e.g., HTML v. JSON requests).

Note that if you prefer, you can configure your controllers to automatically frill all objects for presentation by calling the auto_frill method inside your ApplicationController, instead of manually having to opt them it via the frill method:

class ApplicationController < ActionController::Base
  auto_frill
end

Now, you could remove the frill from your ArticlesController:

class ArticlesController < ApplicationController
  respond_to :json, :html

  def show
    @article = Article.find(params[:id])
    respond_with @article
  end
end

Now, any instance variables you create in your controllers will be automatically frilled before handed off to your views.

If you're using frill inside a Rails application, you can take advantage of the "frill" rspec helper:

require 'spec_helper'

describe HtmlTimestampFrill do
  let(:model) {
    Class.new do
      def created_at
        DateTime.new(2012, 1, 1)
      end
    end.new
  end

  context "html request" do
    subject { frill model }
    its(:created_at) { should == "<b>January 01, 2012 00:00<b>" }
  end

  context "non-html request" do
    subject { frill model, "HTTP_ACCEPT" => "application/json" }
    its(:created_at) { should == "January 01, 2012 00:00" }
  end
end

It will assume an html request context, and it will embue your model with h and helpers methods.

If you're attempting to test the MyFrill.frill? method, you'll need to supply it with stubs:

require 'spec_helper'

describe HtmlTimestampFrill do
  let(:context) { double :view_context }

  subject { HtmlTimestampFrill.frill? double(:model, created_at: "foo"), context }

  context "given an HTML request" do
    before { context.stub_chain(:request, :format, :html?).and_return true }
    it { should be_true }
  end

  context "given a non-HTML request" do
    before { context.stub_chain(:request, :format, :html?).and_return false }
    it { should be_false }
  end
end

Note (2012/09/05): because of a subtle bug in RSpec, the above stub chain stub_chain(:request, :format, :html?) fails on the latest RSpec release (2.11.0) but is fixed in master. See issue #587 and the commit that fixes it.

Since frills are just modules, it's possible to test your frills in relative isolation.

require 'spec_helper'

describe TimestampFrill do
  let(:object) do
    double :object, 
      created_at: DateTime.new(2012, 1, 1),
      h: ApplicationController.new.view_context
  end

  subject { object.extend TimestampFrill }

  its(:created_at) { should == "January 01, 2012 00:00" }
end

When it comes to view methods that render partials, etc., you could choose to test them with integration:

require 'spec_helper'                                                     

class SomeModel
  def h 
    @view_context ||= ApplicationController.new.view_context
  end

  def created_at
     Time.new(2012,1,1)
  end
end   

describe HtmlTimestampFrill do                                            
  let(:object) { SomeModel.new.extend TimestampFrill }

  subject { object.extend HtmlTimestampFrill }     
  
  describe "#created_at" do
    it "should render the timestamp partial" do
      subject.created_at.strip.should == "<b>January 01, 2012 00:00</b>"
    end
  end
end

Or you could test them by stubbing out the view context, and simply setting up expectations on them:

require 'spec_helper'

class SomeModel
  def h; end
  def created_at; end
end
  
describe HtmlTimestampFrill do                                            
  let(:object) { SomeModel.new }
  
  subject { object.extend HtmlTimestampFrill }
  
  describe "#created_at" do                                               
    it "should render the timestamp partial" do
      subject.h.should_receive(:render)
      subject.created_at
    end
  end
end

The latter can be nice if you're really just interested in testing conditional logic inside your decoration.

There are really just three integrations in a Rails app: the frill method inside of your controller, the auto_frill macro for controllers, plus the ability to call view helper methods inside of your module methods.

To kickoff the decoration of an object outside of a Rails application, simply call Frill.decorate:

Frill.decorate my_object, my_context

• Ben Moss
• Nicholas Greenfield

MIT