Presenters Refactoring Example

Ruby on Rails
1

I created this refactoring example for my RailsConf 2014 talk on refactoring fat controllers.

Here is the code for this example:

Please feel free to make comments in the PR or in this message thread. Thanks in advance for any feedback on this topic.

A Name for a PORO

  • Some Object for Complicated controller setup for a view
  • Terminology is controversial in the context of prior literature.
  • Trying to describe a object that sits between a controller method and a view.
  • Could have used “Facade”

But Facade???

Presenter

  • Object used to facilitate presentation of data in the view, typically
    constructed in the controller method or maybe in the view.
  • Smooth sounding.
  • Easy to spell.

Presenter Applicable Situation

  1. Controller is initializing multiple instance variables for the view.
  2. Controller has several private methods supporting the public method
    associated with the action.
  3. View has lots of inline Ruby code for calculating instance variables
  4. Logic is specific to one controller method and one view, or maybe a couple
    different response types for the same controller method.
  5. Numerous view helper methods interacting just for one action.
  6. If you find same code in multiple presenters for same model, then see if you
    can move to a decorator or concern. A module is another option for DRY’ing up
    duplication.

Presenter Solution

  1. Create directory app/presenters and add this code to application.rb 
    config.autoload_paths += %W(
      #{config.root}/app/presenters
    )
  1. Create subdirectory app/presenters/users
  2. Create presenter: User::FollowPresenter
  3. Controller instantiates the User::FollowPresenter that is used by the
    view.
  4. Move ruby code from view and the controller into the presenter.
  5. Possibly include this snippet of code so that view instance methods are
    available:
  include Draper::ViewHelpers

Presenter Advantages

  1. Clearly bundles the code around the work the controller is doing and what the
    view needs.
  2. Simplifies code at the controller and view layers.
  3. Provides the possibility of unit testing the Presenter.
  4. Easy to group related methods and memoize instance variables, which can be
    highly beneficial if fragment caching is used, as compared to instantiating
    instance variables in the controller…
  5. Good place for the calculation of a complicated cache key rather than a view
    helper.

Presenter Disadvantages

There might be simpler techniques than creating another class and object, such
as putting some logic in the Draper decorator or a view helper. A few lines of
inline ruby code may work better than moving this code to a separate class.

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