- Add
gem 'draper'
to yourGemfile
andbundle
- When you generate a resource with
rails g resource YourModel
, you get a decorator automatically! - If
YourModel
already exists, runrails g decorator YourModel
to createYourModelDecorator
- Edit
app/decorators/[your_model]_decorator.rb
using: h
to proxy to Rails/application helpers likeh.current_user
- the name of your decorated model to access the wrapped object like
article.created_at
- Wrap models in your controller with the decorator using:
.find
automatic lookup & wrap ex:ArticleDecorator.find(1)
.decorate
method with a single object or collection, ex:ArticleDecorator.decorate(Article.all)
.new
method with single object ex:ArticleDecorator.new(Article.first)
- Call decorator methods from your view templates
ex:
<%= @article_decorator.created_at %>
If you need common methods in your decorators, create an app/decorators/application_decorator.rb
:
class ApplicationDecorator < Draper::Base
# your methods go here
end
and make your decorators inherit from it. Newly generated decorators will respect this choice and inherit from ApplicationDecorator
.
This gem makes it easy to apply the decorator pattern to domain models in a Rails application. This pattern gives you three wins:
- Replace most helpers with an object-oriented approach
- Filter data at the presentation level
- Enforce an interface between your controllers and view templates.
Why hate normal helpers? In Ruby/Rails we approach everything from an Object-Oriented perspective, then with helpers we get procedural.The job of a helper is to take in data and output a presentation-ready string. We can do that with a decorator.
A decorator wraps an object with presentation-related accessor methods. For instance, if you had an Article
object, then the decorator could override .published_at
to use formatted output like this:
class ArticleDecorator < Draper::Base
decorates :article
def published_at
date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
h.content_tag :span, date + time, :class => 'created_at'
end
end
Have you ever written a to_xml
or to_json
method in your model? Did it feel weird to put presentation logic in your model?
Or, in the course of formatting this data, did you wish you could access current_user
down in the model? Maybe for guests your to_json
is only going to show three attributes, but if the user is an admin they get to see them all.
How would you handle this in the model layer? You'd probably pass the current_user
or some role/flag down to to_json
. That should still feel slimy.
When you use a decorator you have the power of a Ruby object but it's a part of the view layer. This is where your to_json
belongs. You can access your current_user
helper method using the h
proxy available in the decorator:
class ArticleDecorator < ApplicationDecorator
decorates :article
ADMIN_VISIBLE_ATTRIBUTES = [:title, :body, :author, :status]
PUBLIC_VISIBLE_ATTRIBUTES = [:title, :body]
def to_json
attr_set = h.current_user.admin? ? ADMIN_VISIBLE_ATTRIBUTES : PUBLIC_VISIBLE_ATTRIBUTES
article.to_json(:only => attr_set)
end
end
Want to strictly control what methods are proxied to the original object? Use denies
or allows
.
The denies
method takes a blacklist approach. For instance:
class ArticleDecorator < ApplicationDecorator
decorates :article
denies :title
end
Then, to test it:
> ad = ArticleDecorator.find(1)
=> #<ArticleDecorator:0x000001020d7728 @model=#<Article id: 1, title: "Hello, World">>
> ad.title
NoMethodError: undefined method `title' for #<ArticleDecorator:0x000001020d7728>
A better approach is to define a whitelist using allows
:
class ArticleDecorator < ApplicationDecorator
decorates :article
allows :title, :description
end
> ad = ArticleDecorator.find(1)
=> #<ArticleDecorator:0x000001020d7728 @model=#<Article id: 1, title: "Hello, World">>
> ad.title
=> "Hello, World"
> ad.created_at
NoMethodError: undefined method `created_at' for #<ArticleDecorator:0x000001020d7728>
Add the dependency to your Gemfile
:
gem "draper"
Then run bundle
from the project directory.
To decorate a model named Article
:
rails generate decorator article
Open the decorator model (ex: app/decorators/article_decorator.rb
) and add normal instance methods. To access the wrapped source object, use a method named after the decorates
argument:
class ArticleDecorator < Draper::Base
decorates :article
def author_name
article.author.first_name + " " + article.author.last_name
end
end
You probably want to make use of Rails helpers and those defined in your application. Use the helpers
or h
method proxy:
class ArticleDecorator < Draper::Base
decorates :article
def published_at
date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
h.content_tag :span, date + time, :class => 'created_at'
end
end
Hate seeing that h.
proxy all over? Willing to mix a bazillion methods into your decorator? Then try lazy helpers:
class ArticleDecorator < Draper::Base
decorates :article
include Draper::LazyHelpers
def published_at
date = content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
content_tag :span, date + time, :class => 'created_at'
end
end
When writing your controller actions, you have three options:
- Call
.new
and pass in the object to be wrapped
ArticleDecorator.new(Article.find(params[:id]))
- Call
.decorate
and pass in an object or collection of objects to be wrapped:
ArticleDecorator.decorate(Article.first) # Returns one instance of ArticleDecorator
ArticleDecorator.decorate(Article.all) # Returns an enumeration proxy of ArticleDecorator instances
- Call
.find
to automatically do a lookup on thedecorates
class:
ArticleDecorator.find(1)
Use the new methods in your views like any other model method (ex: @article.published_at
):
<h1><%= @article.title %> <%= @article.published_at %></h1>
Using the provided generator, Draper will place specs for your new decorator in spec/decorators/
.
By default, specs in spec/decorators
will be tagged as type => :decorator
. Any spec tagged as decorator
will make helpers available to the decorator.
If your decorator specs live somewhere else, which they shouldn't, make sure to tag them with type => :decorator
. If you don't tag them, Draper's helpers won't be available to your decorator while testing.
Note: If you're using Spork, you need to require 'draper/test/rspec_integration'
in your Spork.prefork block.
Here are some ideas of what you might do in decorator methods:
- Implement output formatting for
to_csv
,to_json
, orto_xml
- Format dates and times using
strftime
- Implement a commonly used representation of the data object like a
.name
method that combinesfirst_name
andlast_name
attributes
Ryan Bates has put together an excellent RailsCast on Draper based on the 0.8.0 release: http://railscasts.com/episodes/286-draper
For a brief tutorial with sample project, check this out: http://tutorials.jumpstartlab.com/topics/decorators.html
Say I have a publishing system with Article
resources. My designer decides that whenever we print the published_at
timestamp, it should be constructed like this:
<span class='published_at'>
<span class='date'>Monday, May 6</span>
<span class='time'>8:52AM</span>
</span>
Could we build that using a partial? Yes. A helper? Uh-huh. But the point of the decorator is to encapsulate logic just like we would a method in our models. Here's how to implement it.
First, follow the steps above to add the dependency and update your bundle.
Since we're talking about the Article
model we'll create an ArticleDecorator
class. You could do it by hand, but use the provided generator:
rails generate decorator Article
Now open up the created app/decorators/article_decorator.rb
and you'll find an ArticleDecorator
class. Add this method:
def published_at
date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = h.content_tag(:span, article.published_at.strftime("%l:%M%p").delete(" "), :class => 'time')
h.content_tag :span, date + time, :class => 'published_at'
end
Then you need to perform the wrapping in your controller. Here's the simplest method:
class ArticlesController < ApplicationController
def show
@article = ArticleDecorator.find params[:id]
end
end
Then within your views you can utilize both the normal data methods and your new presentation methods:
<%= @article.published_at %>
Ta-da! Object-oriented data formatting for your view layer. Below is the complete decorator with extra comments removed:
class ArticleDecorator < Draper::Base
decorates :article
def published_at
date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
h.content_tag :span, date + time, :class => 'published_at'
end
end
Add a decorates_association :association_name
to gain access to a decorated version of your target association.
class ArticleDecorator < Draper::Base
decorates :article
decorates_association :author # belongs_to :author association
end
class AuthorDecorator < Draper::Base
decorates :author
def fancy_name
"#{model.title}. #{model.first_name} #{model.middle_name[0]}. #{model.last_name}"
end
end
Now when you call the association it will use a decorator.
<%= @article.author.fancy_name %>
Draper loads your application's decorators when Rails start. This may lead to an issue with configuring I18n, whereby the settings you provide in ./config/application.rb
are ignored. This happens when you use the I18n
constant at the class-level in one of the models that have a decorator, as in the following example:
# app/models/user.rb
class User < ActiveRecord::Base
validates :email, presence: { message: I18n.t('invalid_email') }
end
# app/decorators/user_decorator.rb
class UserDecorator < ApplicationDecorator
decorates :user
end
Note how the validates
line is executed when the User
class is loaded, triggering the initialization of the I18n framework before Rails had a chance to apply its configuration.
Using I18n
directly in your model definition is an antipattern. The preferred solution would be to not override the message
option in your validates
macro, but provide the activerecord.errors.models.attributes.user.email.presence
key in your translation files.
For automatic decoration, check out decorates_before_rendering.
- Fork it.
- Create a branch (
git checkout -b my_awesome_branch
) - Commit your changes (
git commit -am "Added some magic"
) - Push to the branch (
git push origin my_awesome_branch
) - Send pull request
Draper was conceived by Jeff Casimir and heavily refined by Steve Klabnik and a great community of open source contributors.
- Jeff Casimir ([email protected])
- Steve Klabnik ([email protected])
- Vasiliy Ermolovich
(The MIT License)
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.