draper-decorators

Draper Decorators for Rails

This skill provides guidance for creating effective Draper decorators in Rails applications.

Philosophy

Decorators implement separation of concerns between business logic (models) and presentation logic (views). A decorator wraps a model to add view-specific methods without polluting the model.

What belongs in decorators:

• Date/time formatting (created_at.strftime("%B %d, %Y"))
• String concatenation ("#{first_name} #{last_name}")
• HTML generation (h.content_tag(:span, status, class: css_class))
• Conditional rendering based on state
• Number formatting (currency, percentages)
• CSS class generation based on object state

What does NOT belong in decorators:

• Business logic (validations, calculations, state changes)
• Database queries (use includes in controllers)
• Anything not directly related to presentation

Basic Structure

# app/decorators/user_decorator.rb
class UserDecorator < ApplicationDecorator
  delegate_all

  def full_name
    "#{first_name} #{last_name}"
  end

  def formatted_created_at
    created_at.strftime("%B %d, %Y")
  end

  def status_badge
    css_class = active? ? "badge-success" : "badge-secondary"
    h.content_tag(:span, status, class: "badge #{css_class}")
  end
end

Delegation Strategies

Option 1: delegate_all (Convenient)

Delegates all methods to the wrapped object via method_missing. Use for most decorators.

class ProductDecorator < ApplicationDecorator
  delegate_all

  def formatted_price
    h.number_to_currency(price)
  end
end

Option 2: Explicit Delegation (Strict)

Explicitly declare which methods to delegate. Use for larger apps where control matters.

class ProductDecorator < ApplicationDecorator
  delegate :id, :name, :price, :created_at, :persisted?

  def formatted_price
    h.number_to_currency(price)
  end
end

Accessing the Wrapped Object

Three equivalent ways to access the model:

class ArticleDecorator < ApplicationDecorator
  delegate_all

  def display_title
    object.title.upcase      # via 'object'
    model.title.upcase       # via 'model' (alias)
    article.title.upcase     # via model name (auto-generated)
  end
end