Decorators vs Helpers in Rails?

Question

I'm trying to understand decorator patterns.

As I understand it, Decorators are concerned with 'presenting' the data of a model. They will encompass methods that can be called in the Views.

Up until now, I would have been throwing methods like that in the Helpers or just in the Models (if they need to be called on model instances). Is the main difference between Decorators and Helpers that Decorators are tied to a specific model, whereas Helpers can be more generic utility methods (like Date helpers and so on)?

Answer 1

Rails' (built-in) way of organizing your code is: Fat models, skinny controllers, and throw the rest in Helpers (or Concerns, which are Helpers but for controllers/models).

Biggest problems with helpers (IMO):

• they are accessible in any view. Yep, everything defined in every Helpers of your app is available in the views...
• they are modules: they cannot be instantiated, therefore you call their methods only giving arguments. I prefer the OOP version: @user.full_name.

Decorators:

• basically, they wrap your model's instance and provide methods for display purpose. A Decorator should not modify the data, just arrange it, pluralize, translate, add commas, display currency with the price, etc. It decorates the object and its data.
• they are tied to a specific object (not only model instance, but you can also use a Decorator for a Plain-Old-Ruby-Object as well, such as UserRole or Country).

Using the Decorator pattern will reduce the amount of code in the fat models (imposed by Rails' built-in way to do things):

• Your model, which is supposed to hold the business logic, is not polluted with display logic anymore.
• Your Helpers are no longer big fat piles of methods available anywhere, but instead only defining really globally-helping methods like link_to_icon(icon_name, *args), hours_from_datetime(datetime, format = '24'), menu_link(name, path, *args), etc.