mirror of
https://github.com/drapergem/draper
synced 2023-03-27 23:21:17 -04:00
416 lines
16 KiB
Markdown
416 lines
16 KiB
Markdown
# Draper: View Models for Rails
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[](http://travis-ci.org/jcasimir/draper)
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## Quick Start
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1. Add `gem 'draper'` to your `Gemfile` and `bundle`
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2. When you generate a resource with `rails g resource YourModel`, you get a decorator automatically!
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3. If YourModel exists, run `rails g decorator YourModel`
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4. Edit `app/decorators/[your_model]_decorator.rb` using:
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1. `h` to proxy to Rails/application helpers like `h.current_user`
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2. `[your_model]` to access the wrapped object like `article.created_at`
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5. Wrap models in your controller with the decorator using:
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1. `.find` automatic lookup & wrap
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ex: `ArticleDecorator.find(1)`
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2. `.decorate` method with single object or collection,
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ex: `ArticleDecorator.decorate(Article.all)`
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3. `.new` method with single object
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ex: `ArticleDecorator.new(Article.first)`
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6. Output the instance methods in your view templates
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ex: `@article_decorator.created_at`
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If you need common methods in your decorators, create an `app/decorators/application_decorator.rb`:
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``` ruby
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class ApplicationDecorator < Draper::Base
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# your methods go here
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end
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```
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and make your decorators inherit from it. Newly generated decorators will respect this choice and inherit from `ApplicationDecorator`.
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## Watch the RailsCast
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Ryan Bates has put together an excellent RailsCast on Draper based on the 0.8.0 release:
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[](http://railscasts.com/episodes/286-draper)
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## What's New
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Check out the full commit history at http://github.com/jcasimir/draper/commits
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In summary, you can now:
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* [Namespace the `decorates` call](https://github.com/jcasimir/draper/commit/1c3d5667b8406b80b490d876257379087b129f92)
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* [Use your decorators with CanCan](https://github.com/jcasimir/draper/commit/ac1f3083989107d877e2b1c918c3a3e792db99e8)
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* [Use a more generalized `options` hash in decorator initialization](https://github.com/jcasimir/draper/commit/03910877d0461356da0968a87346592908f292a7)
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* [Get better performance by generating methods](https://github.com/jcasimir/draper/commit/ebe30511b79eac82276413ca7ae54a4a4d86d4dc)
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* [Automatically decorate associated objects](https://github.com/jcasimir/draper/commit/1580baa287997ed4e356aae0ffeeb8fe9c326ced) See Example near bottom of Readme
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Thanks to [steveklabnik](http://github.com/steveklabnik), [i0rek](http://github.com/i0rek), [laserlemon](http://github.com/laserlemon), [michaelfairley](http://github.com/michaelfairley), [dnagir](http://github.com/dnagir), [ubermajestix](http://github.com/ubermajestix), [tmaier](http://github.com/tmaier), [angelim](http://github.com/angelim), [duncanbeevers](http://github.com/duncanbeevers), Albert Peng & JR Boyens, [leocassarani](http://github.com/leocassarani), [Jeff Felchner](http://github.com/Felchner), [shingara](http://github.com/shingara), [momolog](http://github.com/momolog), and [ayamomiji](http://github.com/ayamomiji) for their contributions to this version!
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## Goals
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This gem makes it easy to apply the decorator pattern to domain models in a Rails application. This pattern gives you three wins:
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1. Replace most helpers with an object-oriented approach
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2. Filter data at the presentation level
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3. Enforce an interface between your controllers and view templates.
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### 1. Object Oriented Helpers
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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.
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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:
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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def published_at
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date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
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time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
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h.content_tag :span, date + time, :class => 'created_at'
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end
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end
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```
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### 2. View-Layer Data Filtering
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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?
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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.
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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.
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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:
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```ruby
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class ArticleDecorator < ApplicationDecorator
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decorates :article
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ADMIN_VISIBLE_ATTRIBUTES = [:title, :body, :author, :status]
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PUBLIC_VISIBLE_ATTRIBUTES = [:title, :body]
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def to_json
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attr_set = h.current_user.admin? ? ADMIN_VISIBLE_ATTRIBUTES : PUBLIC_VISIBLE_ATTRIBUTES
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article.to_json(:only => attr_set)
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end
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end
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```
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### 3. Enforcing an Interface
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Want to strictly control what methods are proxied to the original object? Use `denies` or `allows`.
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#### Using `denies`
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The `denies` method takes a blacklist approach. For instance:
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```ruby
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class ArticleDecorator < ApplicationDecorator
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decorates :article
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denies :title
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end
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```
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Then, to test it:
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```irb
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> ad = ArticleDecorator.find(1)
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=> #<ArticleDecorator:0x000001020d7728 @model=#<Article id: 1, title: "Hello, World">>
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> ad.title
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NoMethodError: undefined method `title' for #<ArticleDecorator:0x000001020d7728>
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```
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#### Using `allows`
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A better approach is to define a whitelist using `allows`:
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```ruby
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class ArticleDecorator < ApplicationDecorator
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decorates :article
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allows :title, :description
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end
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```
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```irb
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> ad = ArticleDecorator.find(1)
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=> #<ArticleDecorator:0x000001020d7728 @model=#<Article id: 1, title: "Hello, World">>
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> ad.title
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=> "Hello, World"
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> ad.created_at
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NoMethodError: undefined method `created_at' for #<ArticleDecorator:0x000001020d7728>
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```
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## Up and Running
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### Setup
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Add the dependency to your `Gemfile`:
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```
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gem "draper"
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```
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Then run `bundle` from the project directory.
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### Generate the Decorator
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To decorate a model named `Article`:
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```
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rails generate decorator article
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```
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### Writing Methods
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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:
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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def author_name
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article.author.first_name + " " + article.author.last_name
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end
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end
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```
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### Using Existing Helpers
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You probably want to make use of Rails helpers and those defined in your application. Use the `helpers` or `h` method proxy:
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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def published_at
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date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
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time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
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h.content_tag :span, date + time, :class => 'created_at'
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end
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end
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```
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#### Lazy Helpers
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Hate seeing that `h.` proxy all over? Willing to mix a bazillion methods into your decorator? Then try lazy helpers:
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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include Draper::LazyHelpers
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def published_at
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date = content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
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time = content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
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content_tag :span, date + time, :class => 'created_at'
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end
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end
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```
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### In the Controller
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When writing your controller actions, you have three options:
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* Call `.new` and pass in the object to be wrapped
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```ruby
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ArticleDecorator.new(Article.find(params[:id]))
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```
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* Call `.decorate` and pass in an object or collection of objects to be wrapped:
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```ruby
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ArticleDecorator.decorate(Article.first) # Returns one instance of ArticleDecorator
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ArticleDecorator.decorate(Article.all) # Returns an enumeration proxy of ArticleDecorator instances
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```
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* Call `.find` to automatically do a lookup on the `decorates` class:
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```ruby
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ArticleDecorator.find(1)
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```
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### In Your Views
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Use the new methods in your views like any other model method (ex: `@article.published_at`):
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```erb
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<h1><%= @article.title %> <%= @article.published_at %></h1>
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```
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### Using in Mailers
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To use decorators in mailers that use helpers, you have to call `set_current_view_context` in your
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ActionMailer class.
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```ruby
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class ArticleMailer < ActionMailer::Base
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default 'init-draper' => Proc.new { set_current_view_context }
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end
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```
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### Integration with RSpec
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Using the provided generator, Draper will place specs for your new decorator in `spec/decorators/`.
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By default, specs in `spec/decorators` will be tagged as `type => :decorator`. Any spec tagged as `decorator` will run `ApplicationController.new.set_current_view_context` which makes helpers available to the decorator.
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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.
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Note: If you're using Spork, you need to `require 'draper/rspec_integration'` in your Spork.prefork block.
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## Possible Decoration Methods
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Here are some ideas of what you might do in decorator methods:
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* Implement output formatting for `to_csv`, `to_json`, or `to_xml`
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* Format dates and times using `strftime`
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* Implement a commonly used representation of the data object like a `.name` method that combines `first_name` and `last_name` attributes
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## Example Using a Decorator
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For a brief tutorial with sample project, check this out: http://tutorials.jumpstartlab.com/topics/decorators.html
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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:
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```html
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<span class='published_at'>
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<span class='date'>Monday, May 6</span>
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<span class='time'>8:52AM</span>
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</span>
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```
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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.
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First, follow the steps above to add the dependency and update your bundle.
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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:
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```
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rails generate decorator Article
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```
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Now open up the created `app/decorators/article_decorator.rb` and you'll find an `ArticleDecorator` class. Add this method:
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```ruby
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def published_at
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date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
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time = h.content_tag(:span, article.published_at.strftime("%l:%M%p").delete(" "), :class => 'time')
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h.content_tag :span, date + time, :class => 'published_at'
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end
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```
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Then you need to perform the wrapping in your controller. Here's the simplest method:
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```ruby
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class ArticlesController < Draper::Decorator
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def show
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@article = ArticleDecorator.find params[:id]
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end
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end
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```
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Then within your views you can utilize both the normal data methods and your new presentation methods:
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```ruby
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<%= @article.published_at %>
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```
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Ta-da! Object-oriented data formatting for your view layer. Below is the complete decorator with extra comments removed:
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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def published_at
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date = h.content_tag(:span, article.published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
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time = h.content_tag(:span, article.published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
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h.content_tag :span, date + time, :class => 'published_at'
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end
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end
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```
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### Example of Decorated Associations
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Add a `decorates_association :association_name` to gain access to a decorated version of your target association.
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```ruby
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class ArticleDecorator < Draper::Base
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decorates :article
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decorates_association :author # belongs_to :author association
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end
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class AuthorDecorator < Draper::Base
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decorates :author
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def fancy_name
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"#{model.title}. #{model.first_name} #{model.middle_name[0]}. #{model.last_name}"
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end
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end
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```
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Now when you call the association it will use a decorator.
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```ruby
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<%= @article.author.fancy_name %>
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```
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### A note on Rails configuration
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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:
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```ruby
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# app/models/user.rb
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class User < ActiveRecord::Base
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validates :email, presence: { message: I18n.t('invalid_email') }
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end
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# app/decorators/user_decorator.rb
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class UserDecorator < ApplicationDecorator
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decorates :user
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end
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```
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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.
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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.
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## Contributing
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1. Fork it.
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2. Create a branch (`git checkout -b my_awesome_branch`)
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3. Commit your changes (`git commit -am "Added some magic"`)
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4. Push to the branch (`git push origin my_awesome_branch`)
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5. Send pull request
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## Issues / Pending
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* Documentation
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* Add more information about using "context"
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* Add information about the `.decorator` method
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* Make clear the pattern of overriding accessor methods of the wrapped model
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* Build sample Rails application(s)
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* Generators
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* Implement hook so generating a controller/scaffold generates a decorator
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* Add generators for...
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* `draper:model`: Model + Decorator
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* `draper:controller`: Controller setup with decoration calls
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* `draper:scaffold`: Controller, Model, Decorator, Views, Tests
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* Other
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* Implement a HATEOAS helper, maybe as a separate gem
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* Build a fly website like http://fabricationgem.com
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## License
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(The MIT License)
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Copyright © 2011 Jeff Casimir
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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:
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The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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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.
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