Presenter Pattern for Rails Applications
gem install classic_presenter
In your Gemfile you should set:
Create a simple ActiveRecord class that you want to present:
class Product < ActiveRecord::Base end
Create a presenter class inheriting from ClassicPresenter::Base:
class ProductPresenter < ClassicPresenter::Base def display_name if context.user_logged_in? name else context.link_to name, context.product_path end end def display_description context.render "products/description", :product => self end end
In your view, show.html.erb for example, you can present your Product object using this syntax:
<% present ProductPresenter, @product do |presenter| %> <%= presenter.display_name %> <%= presenter.display_description %> <% end %>
You can decorates a collection of objects with your presenter:
#products_controller.rb @products = ProductPresenter.map(Post.all, view_context)
Inside of the presenter we have an access to the context. In the example above the context is the View(ActionView), then we can access any method like link_to, number_to_currency etc directly.
You can also instantiate your presenter in the controller using the view_context and then to access any helper method like number_to_currency:
#products_controller.rb @product = ProductPresenter.new(Product.find(params[:id]), view_context) class ProductPresenter < ClassicPresenter::Base def price context.number_to_currency(price, :precision => 3) end end
Since ClassicPresenter::Base is a Decorator, it implements the “transparent interface” requirements of the Gang of Four’s definition. This means that when we call some method in ProductPresenter, it will be delegated to the decorated object (in this case Product), like this:
#products_controller.rb @product = ProductPresenter.new(Product.find(params[:id])) #show.html.erb <%= @product.name %> <%= @product.display_name %>
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