Design Pattern: Presenter

Philosophy

• Views are for presentation.
• There should be no ActiveRecord queries in views.
• Most logic (if statements) should be excluded from views.

Why Not Helpers?

Helpers are better to use if you have a global formatting method that you re-use in different views.

Things like:

• rendering markdown
• showing dates in a specific format
• removing specific words from text

Helpers are not great to overuse because they lack organization and are difficult to reuse across your app.

Using Presenter Objects

• create app/presenters.
• name after model, app/presenters/post_presenter.rb.

class PostPresenter
  def initialize(post)
    @post = post
  end

  def title_without_forbidden_words
    @post.title.gsub("forbidden word", "")
  end

  def css_color
    @post.draft? ? "orange" : "green"
  end
end

<% presenter = PostPresenter.new(post) %>

<p>
  Post title: <%= presenter.title_without_forbidden_words %>

  <%= link_to "Read post", post, class: "w-75 p-3 text-#{presenter.css_color} border-#{presenter.css_color}" %>
</p>

This accomplishes a few things:

• it removes logic from views
• creates meaningful names for methods and logic
• allows logic to more easily be reused in other views and mailers

Rails Design Patterns: Presenter & Service Objects