DocumentPresenter has a view_context, not a controller

[flyingzumwalt]

The Pattern

A Presenter is a class that is aware of both your Model and your View. Your ApplicationHelper should create these instances by calling MyPresenter.new(object, self), meaning that template within the Presenter is a reference to the view rendering context, giving you access to all of the helper methods that would be available in a view template.

class MyPresenter
  def initialize(object, view_context)
    @object = object
    @view_context = view_context
  end
end

you initialize it like this from a presenter helper method, where the helper method passes self into the presenter. In a View Helper, self is a view context. You could call it view_context, template, or helper. It is not a Controller.

module ApplicationHelper
  def presenter(object)
    presenter_class.new(object, self)
  end
end

Blacklight::DocumentPresenter uses the wrong names to do the right thing

In [app/helpers/concerns/blacklight_helper_behavior.rb]

##
# Returns a document presenter for the given document
def presenter(document)
  presenter_class.new(document, self)
end

This matches with the canonical implementation of this pattern. The second argument is a view context, not a controller. This doesn't match with what the DocumentPresenter says it expects: [app/presenters/blacklight/document_presenter.rb]

# @param [SolrDocument] document
# @param [ActionController::Base] controller scope for linking and generating urls
# @param [Blacklight::Configuration] configuration
def initialize(document, controller, configuration = controller.blacklight_config)
  @document = document
  @configuration = configuration
  @controller = controller
end

The DocumentPresenter is mis-naming that variable and the documentation on that class is incorrect. It claims to want an ActionController::Base as its second argument and calls it "@controller" but really it's getting a view_context, which is what it should be getting, and it should call it either view_context, template, or helper.

References

http://nithinbekal.com/posts/rails-presenters/
http://railscasts.com/episodes/287-presenters-from-scratch?autoplay=true

[flyingzumwalt]

Note: Even the tests call it a request_context, not controller.

# spec/presenters/document_presenter_spec.rb#L5-9
let(:request_context) { double }
let(:presenter) { Blacklight::DocumentPresenter.new(document, request_context, config) }