RailsConf: Draper Decorators

[justin808]

RailsConf 2014 Talk, Tuesday, 2:30, Ballroom 4, Concerns, Decorators, Presenters, Service Objects, Helpers, Help Me Decide!

Draper Decorator

Code: Github Fat Code Refactoring Techniques Pull Request Draper

Example: Added Draper Decorator class MicropostDecorator. Method posted_ago dries up code in 2 views.

Why?

1. You're putting presentation code in your model or model-concerns.
2. You want to organize some helper methods by models.
3. You've got logic in your controllers/views that is strictly related to
   one model, but multiple controllers/views.
4. You need a good place to consolidate the creation of flash messages related
   to a given model.

To quote the Draper Readme:

Decorators are the ideal place to:

• format complex data for user display
• define commonly-used representations of an object, like a name method that
  combines first_name and last_name attributes
• mark up attributes with a little semantic HTML, like turning a url field
  into a hyperlink

What?

• Draper is a popular gem that facilitates model decorators.
• Easy to use formula for introducing decorators in your application.
• Simple to include like Concerns.
• Widely used in the Rails community.
• drapergem/draper on github
• Railscasts Draper Episode

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.
4. Put h. in front of calls to helpers.
5. Remove references to the model in the decorator, as the method is
   essentially on the model.
6. 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.