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concern_pattern_composition

🤝 Entity Composition with Concern Patterns​

Rails’ ActiveSupport::Concern simplifies module inclusion, dependency declaration, and shared logic. Use included and ClassMethods within concerns to compose features across models or controllers with minimal friction.

module Taggable
  extend ActiveSupport::Concern

  included do
    has_many :taggings
    has_many :tags, through: :taggings
  end

  def tag_list
    tags.map(&:name).join(', ')
  end
end

class Article < ApplicationRecord
  include Taggable
end

Concerns enforce order of inclusion and avoid common mixin pitfalls.