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.