# Draper: View Models for Rails ![TravisCI Build Status](https://secure.travis-ci.org/jcasimir/draper.png) ## Quick Start 1. Add `gem 'draper'` to your `Gemfile` and `bundle` 2. Run `rails g draper:decorator YourModel` 3. Edit `app/decorators/[your_model]_decorator.rb` using: 1. `h` to proxy to Rails/application helpers like `h.current_user` 2. `[your_model]` to access the wrapped object like `article.created_at` 4. Put common decorations in `app/decorators/application.rb` 5. Wrap models in your controller with the decorator using: 1. `.find` automatic lookup & wrap ex: `ArticleDecorator.find(1)` 2. `.decorate` method with single object or collection, ex: `ArticleDecorator.decorate(Article.all)` 3. `.new` method with single object ex: `ArticleDecorator.new(Article.first)` 6. Output the instance methods in your view templates ex: `@article_decorator.created_at` ## Watch the RailsCast Ryan Bates has put together an excellent RailsCast on Draper based on the 0.8.0 release: [![RailsCast #286](https://img.skitch.com/20111021-dgxmqntq22d37fthky6pttk59n.jpg "RailsCast #286 - Draper")](http://railscasts.com/episodes/286-draper) ## What's New ### Version 0.9.X * `.4`: Improved the collection proxy's `respond_to` and `to_ary` to play nicely with Rails' `render` * `.3`: Helpers are available from the decorator class level, so you could write a `ArticleDecorator.new_article_link` that uses `h.link_to` * `.2`: Automatically generate a named accessor for the wrapped object, so now inside of `ArticleDecorator` you can use `article` instead of just `model` * `.2`: Automatically generate RSpec/Test::Unit stub for decorator class * `.1`: Removed the `lazy_helpers` method to favor using `include Draper::LazyHelpers` * `.1`: Refactored how methods are selected for delegation to the wrapped model * `.0`: Fixed how the view context is stored to resolve cross-request issues * `.0`: Decorated collections now return a collection proxy instead of an array, which fixes many compatibility issues ## Goals This gem makes it easy to apply the decorator pattern to domain models in a Rails application. This pattern gives you three wins: 1. Replace most helpers with an object-oriented approach 2. Filter data at the presentation level 3. Enforce an interface between your controllers and view templates. ### 1. Object Oriented Helpers 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: ```ruby class ArticleDecorator < ApplicationDecorator 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 ``` ### 2. View-Layer Data Filtering 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: ```ruby 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 ``` ### 3. Enforcing an Interface Want to strictly control what methods are proxied to the original object? Use `denies` or `allows`. #### Using `denies` The `denies` method takes a blacklist approach. For instance: ```ruby class ArticleDecorator < ApplicationDecorator decorates :article denies :title end ``` Then, to test it: ```irb > ad = ArticleDecorator.find(1) => #> > ad.title NoMethodError: undefined method `title' for # ``` #### Using `allows` A better approach is to define a whitelist using `allows`: ```ruby class ArticleDecorator < ApplicationDecorator decorates :article allows :title, :description end ``` ```irb > ad = ArticleDecorator.find(1) => #> > ad.title => "Hello, World" > ad.created_at NoMethodError: undefined method `created_at' for # ``` ## Up and Running ### Setup Add the dependency to your `Gemfile`: ``` gem "draper" ``` Then run `bundle` from the project directory. ### Generate the Decorator To decorate a model named `Article`: ``` rails generate draper:decorator Article ``` ### Writing Methods 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: ```ruby class ArticleDecorator < ApplicationDecorator decorates :article def author_name article.author.first_name + " " + article.author.last_name end end ``` ### Using Existing Helpers You probably want to make use of Rails helpers and those defined in your application. Use the `helpers` or `h` method proxy: ```ruby class ArticleDecorator < ApplicationDecorator 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 ``` #### Lazy Helpers Hate seeing that `h.` proxy all over? Willing to mix a bazillion methods into your decorator? Then try lazy helpers: ```ruby class ArticleDecorator < ApplicationDecorator 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 ``` ### In the Controller When writing your controller actions, you have three options: * Call `.new` and pass in the object to be wrapped ```ruby ArticleDecorator.new(Article.find(params[:id]))` ``` * Call `.decorate` and pass in an object or collection of objects to be wrapped: ```ruby ArticleDecorator.decorate(Article.first) # Returns one instance of ArticleDecorator ArticleDecorator.decorate(Article.all) # Returns an enumeration proxy of ArticleDecorator instances ``` * Call `.find` to do automatically do a lookup on the `decorates` class: ```ruby ArticleDecorator.find(1) ``` ### In Your Views Use the new methods in your views like any other model method (ex: `@article.published_at`): ```erb

<%= @article.title %> <%= @article.published_at %>

``` ### Using in Mailers To use decorators in mailers that use helpers, you have to call `set_current_view_context` in your mailer method: ```ruby class ActicleMailer < ActionMailer::Base def new_article(article) set_current_view_context @article_decorator = ArticleDecorator.decorate(article) mail(:to => 'come@me.bro', :subject => "New Article: #{@article_decorator.title}") end end ``` ## Possible Decoration Methods Here are some ideas of what you might do in decorator methods: * Implement output formatting for `to_csv`, `to_json`, or `to_xml` * Format dates and times using `strftime` * Implement a commonly used representation of the data object like a `.name` method that combines `first_name` and `last_name` attributes ## Example Using a Decorator For a brief tutorial with sample project, check this out: http://tutorials.jumpstartlab.com/rails/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: ```html Monday, May 6 8:52AM ``` 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 draper:decorator Article ``` Now open up the created `app/decorators/article_decorator.rb` and you'll find an `ArticleDecorator` class. Add this method: ```ruby 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: ```ruby 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: ```ruby <%= @article.published_at %> ``` Ta-da! Object-oriented data formatting for your view layer. Below is the complete decorator with extra comments removed: ```ruby class ArticleDecorator < ApplicationDecorator 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 ``` ## Issues / Pending * Documentation * Add more information about using "context" * Add information about the `.decorator` method * Make clear the pattern of overriding accessor methods of the wrapped model * Build sample Rails application(s) * Add a section about contributing * Generators * Implement hook so generating a controller/scaffold generates a decorator * Add generators for... * `draper:model`: Model + Decorator * `draper:controller`: Controller setup with decoration calls * `draper:scaffold`: Controller, Model, Decorator, Views, Tests * Other * Implement a HATEOAS helper, maybe as a separate gem * Build a fly website like http://fabricationgem.com ## License (The MIT License) Copyright © 2011 Jeff Casimir 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.