Use WeakRef to allow ActiveRecords to be collected, but allow the ActiveRecord to be recreated when needed. Allows a module, class, or instance to keep track of its own metadata without constantly having the metadata in memory and allowing the metadata to be reused without needing pass it through all the cache construction.

metasploit_module.rb

  resurrecting_attr_accessor :module_ancestor do
    ActiveRecord::Base.connection_pool.with_connection do
      Mdm::Module::Ancestor.where(real_path_sha1_hex_digest: real_path_sha1_hex_digest).first
    end
  end

resurrecting_attribute.rb

module Metasploit::Framework::ResurrectingAttribute
  def resurrecting_attr_accessor(attribute_name, &block)
    instance_variable_name = "@#{attribute_name}".to_sym
    getter_name = attribute_name
    setter_name = "#{attribute_name}="

    define_method(getter_name) do
      begin
        strong_reference = nil
        weak_reference = instance_variable_get instance_variable_name

        if weak_reference
          strong_reference = weak_reference.__getobj__
        else
          strong_reference = instance_exec(&block)

          send(setter_name, strong_reference)
        end
      rescue WeakRef::RefError
        # try again by rebuild because __getobj__ failed on the weak_reference because the referenced object was garbage
        # collected.
        instance_variable_set instance_variable_name, nil

        retry
      end

      # Return strong reference so consuming code doesn't have to handle the weak_reference being garbase collected.
      strong_reference
    end

    define_method(setter_name) do |strong_reference|
      weak_reference = WeakRef.new(strong_reference)
      instance_variable_set instance_variable_name, weak_reference
    end
  end
end