Why hate 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 job in an OO style with a decorator.
In general, a decorator wraps an object with presentation-related accessor methods. For instance, if you had an `Article` object, then a decorator might add instance methods like `.formatted_published_at` or `.formatted_title` that output actual HTML.
date = content_tag(:span, published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = content_tag(:span, published_at.strftime("%l:%M%p"), :class => 'time').delete(" ")
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 what is essentially view 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_xml` belongs. It has access to the core data from the model, but it also knows about `current_user` because it can see the `ApplicationHelper` where that method is typically defined.
A proper interface defines a contract between two objects. One purpose of the decorator pattern is to define an interface between your data model and the view template.
You are provided class methods `allows` and `denies` to control exactly which of the subject's methods are available. By default, *all* of the subject's methods can be accessed.
For example, say you want to prevent access to the `:title` method. You'd use `denies` like this:
```ruby
class ArticleDecorator <Draper::Base
denies :title
end
```
`denies` uses a blacklist approach. Note that, as of the current version, denying `:title` does not affect related methods like `:title=`, `:title?`, etc.
A better idea is a whitelist approach using `allows`:
```ruby
class ArticleDecorator <Draper::Base
allows :title, :body, :author
end
```
Now only those methods and any defined in the decorator class itself can be accessed directly.
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
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
<spanclass='published_at'>
<spanclass='date'>Monday, May 6</span>
<spanclass='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, update your bundle, then run the `rails generate decorator:setup` to prepare your app.
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:model Article
```
Now open up the created `app/decorators/article_decorator.rb` and you'll find an `ArticleDecorator` class. Add this method:
```ruby
def formatted_published_at
date = content_tag(:span, published_at.strftime("%A, %B %e").squeeze(" "), :class => 'date')
time = content_tag(:span, published_at.strftime("%l:%M%p").delete(" "), :class => 'time')
content_tag :span, date + time, :class => 'published_at'
end
```
*ASIDE*: Unfortunately, due to the current implementation of `content_tag`, you can't use the style of sending the content is as a block or you'll get an error about `undefined method 'output_buffer='`. Passing in the content as the second argument, as above, works fine.
Then you need to perform the wrapping in your controller. Here's the simplest method:
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