justin808/fat-code-refactoring-techniques — pull request #4 by justin808 (2014-04-05 02:44:34+00:00)
Title: Decorators

# Draper Decorator

- Easy to use formula for introducing decorators in your application.
- Simple to include like Concerns.
- Widely used in the Rails community.
- Works for me!
- [drapergem/draper on github](https://github.com/drapergem/draper)
- [Railscasts Draper Episode](http://railscasts.com/episodes/286-draper)

# Draper Steps

1. Add `gem 'draper'= and run =bundle`
2. Run Draper generator: `rails generate decorator User`, which creates
`app/decorators/user_decorator.rb` and
`spec/decorators/user_decorator_spec.rb`.
3. Move presentation specific view code to decorator.
1. Put `h.` in front of calls to helpers.
2. Remove references to the model in the decorator, as the method is
essentially on the model.
3. Call `model.decorate` to get a decorated instance of the model.

# Draper Applicable Situations

1. Extension to model that only applies to views and presentation.
2. Calculations done in view using model object.
3. Code in view helper that is more closely aligned with the model.
4. Code is that seems relatively general as opposed to clearly useful in only
one view.
5. If method feels relatively generic for views, but specific for a given model,
then the decorator is a good place to put the method.

# Draper Advantages

1. Relatively simple way to add functionality to the model that only applies to the
connection of the model to the view.
2. Can separate presentation specific code from the model.
3. Methods added to the model via the decorator have access to both view helper
methods as well as the model.
4. It's super easy to automatically convert the retrieved model object into it's
decorated instance, either manually or automatically, at the controller
layer.
5. Simple to find the decorator methods, such as using for verification in
feature specs.

# Draper Disadvantages

1. Shares similar problems with concerns in that the model object is still
getting fatter.
2. If there's multiple methods needed for some complex logic, that should be
broken into it's own PORO.
3. The advantage of ease of adding more methods can also be a disadvantage in
that the Decorator can turn into a junk-drawer of loosely coupled methods.