class_cache_key.rb

# frozen_string_literal: true
module ClassCacheKey
  extend ActiveSupport::Concern

  module ClassMethods
    def cache_key(scope = all)
      timestamp = DateTime.new(scope.maximum(:updated_at).to_i).utc.to_s(:number)
      scope_sql = Digest::SHA1.hexdigest(scope.to_sql)
      "#{model_name.cache_key}::#{scope_sql}\##{scope.count}-#{timestamp}"
    end
  end
end

class_cache_key_spec.rb

# frozen_string_literal: true
require 'rails_helper'

RSpec.describe ClassCacheKey, type: :concern do
  let(:active_record_klass) { CHANGE_ME }
  let!(:instance_one) { create(active_record_klass.name.downcase.to_sym) }
  let!(:instance_two) { create(active_record_klass.name.downcase.to_sym) }

  it 'makes a key different per sql statement' do
    expect(active_record_klass.cache_key).not_to eq active_record_klass.order(:created_at).cache_key
  end

  it 'generates a different key after record update' do
    active_record_klass.uncached do
      expect do
        sleep 1
        instance_one.touch
      end.to change(active_record_klass, :cache_key)
    end
  end

  it 'generates a different key after record addition' do
    expect do
      create(active_record_klass.name.downcase.to_sym)
    end.to change(active_record_klass, :cache_key)
  end

  it 'generates a different key after record deletion' do
    expect do
      instance_one.destroy
    end.to change(active_record_klass, :cache_key)
  end
end