Earlier Draft: Draper Decorators

[justin808]

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
• Railscasts Draper Episode

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.
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.

[jodosha]

Another downside is the way a developer have access to the presenter: @model.decorate vs UserDecorator.new(@user). It adds another responsibility to AR models: they are aware of the decoration logic.

That #decorate API is an handy solution do a bigger problem: the lack of separation between views and templates in Rails. A View, should be the place where to initialize a decorator and then the template can use it <%= decorator.formatted_followers_count %>.