Using Presenters in rails

Question

json = JSON.parse(response.body)
    @games = json['machine-games']

    paging = json['paging']
    if paging
      if paging['next']
        next_page_query = paging['next'].match(/\?.*/)[0]
      @next_page = "/machine_games/search#{next_page_query}"
    end

    if paging['previous']
      previous_page_query = paging['previous'].match(/\?.*/)[0]
      @previous_page = "/machine_games/search#{previous_page_query}"
    end
  end

The above is a small piece of logic from the show method in controller.How do i move it to the presenter so that it would hold the machine_games JSON response and provide methods to access the games and next/previous page links (and whether or not they exist). {not that familiar with using presenter pattern}

Answer 1

Let's create a presenter for parsing a JSON response into @games, @next_page and @previous_page.

# app/presenters/games_presenter.rb

class GamesPresenter

  attr_reader :games, :next_page, :previous_page

  def initialize json
    @games = json['machine-games']

    paging = json['paging']
    if paging && paging['next']
      next_page_query = paging['next'].match(/\?.*/)[0]
      @next_page = "/machine_games/search#{next_page_query}"
    end

    if paging && paging['previous']
      previous_page_query = paging['previous'].match(/\?.*/)[0]
      @previous_page = "/machine_games/search#{previous_page_query}"
    end
  end

end

Now your controller action should look something like this:

def show
  # ...
  @presenter = GamesPresenter.new(json)
end

And you can use it in your views:

<% @presenter.games.each do |game| %>
  ...
<% end %>

<%= link_to "Previous", @presenter.previous_page %>
<%= link_to "Next", @presenter.next_page %>

And in order to tell Rails to load the apps/presenters/ directory along with models/, controllers/, views/, etc. add this to config/application.rb:

config.after_initialize do |app|
  app.config.paths.add 'app/presenters', :eager_load => true
end