Lazy Load CanCanCan Abilities In Rails

readme.md

This Rails strategy lets you lazy load your CanCanCan abilities so you only load them when needed helping improve overall performance. Full blog post at https://dalezak.medium.com/lazy-load-cancancan-abilities-in-rails-d9a4c93149c7.

application_controller.rb

def current_ability
  @current_ability ||= begin
    current_ability = Ability.new(current_user)
    controller_names.to_a.each do |controller_name|
      model_name = controller_name.classify
      model_ability = "#{model_name}Ability".constantize rescue nil
      if model_ability.present? && model_abilities[model_ability].nil?
        model_abilities[model_ability] = model_ability.new(current_user)
        current_ability.merge(model_abilities[model_ability])
      end
    end
    current_ability
  end
end

def can?(*args)
  merge_ability(args[1])
  current_ability.can?(*args)
end 

def cannot?(*args)
  merge_ability(args[1])
  current_ability.cannot?(*args)
end

def authorize!(*args)
  merge_ability(args[1])
  current_ability.authorize!(*args)
end

def model_abilities
  @model_abilities ||= {}
end  

def controller_names
  @controller_names ||= begin
    regex_digit = /\d/
    regex_uuid = /[a-f0-9]{8}-([a-f0-9]{4}-){3}[a-f0-9]{12}/
    controller_names = request.path.split("/")
    controller_names = controller_names.reject { |p| p.match?(regex_uuid) || p.match?(regex_digit) || p.empty? }
    controller_names = controller_names.map{ |p| File.basename(p, File.extname(p))}
    if controller_names.include?(controller_name)
      controller_names = controller_names.take(controller_names.index(controller_name)+1)
    end
  end  
end

def merge_abilities(*model_names)
  model_names.each do |model_name|
    merge_ability(model_name.to_s)
  end  
end  

def merge_ability(model)
  model_name = model.is_a?(Class) ? model.name : model.class.name
  model_ability = "#{model_name}Ability".constantize rescue nil
  if model_ability.present? && model_abilities[model_ability].nil?
    model_abilities[model_ability] = model_ability
    current_ability.merge(model_ability.new(current_user))
  end
end 

model_ability.rb

class ModelAbility
  include CanCan::Ability

  def initialize(user)
    if user.nil?
      self.user(user)
    elsif user.is_a?(Admin)
      self.admin(user)
    end  
  end
  
  def admin(user)
  end
  
  def user(user)
  end
  
end  

post_ability.rb

class PostAbility < ModelAbility

  def admin(user)
    can :manage, Post
  end

  def user(user)
    can :create, Post
    can :read, Post
    can :update, Post, user_id: user.id
  end

end